I see this in the 'dots' gimp-perl script.  The PDB trace is shown below, along
with each step.  I ran this on a new image of size 377x233 if that matters. 

 DB<1> b 35
  DB<2> c
main::CODE(0x83e47a0)(/usr/local/lib/gimp/2.0/plug-ins/dots:35):
35:        
my($img,$layer,$size,$dotcolor,$opacity,$xspacing,$yspacing,$xoffset,$yoffset) =@_;
  DB<2> n
main::CODE(0x83e47a0)(/usr/local/lib/gimp/2.0/plug-ins/dots:36):
36:         my $has_noselection;
  DB<2> n
main::CODE(0x83e47a0)(/usr/local/lib/gimp/2.0/plug-ins/dots:37):
37:         $layer->is_layer || die "A layer is required for this plugin";
  DB<2> n
gimp_drawable_is_layer(
        DRAWABLE drawable=2     "The drawable"
        ) = (
        INT32 layer=1   "Non-zero if the drawable is a layer"
        )
main::CODE(0x83e47a0)(/usr/local/lib/gimp/2.0/plug-ins/dots:39):
39:         $yoffset = $yoffset % $yspacing;
  DB<2> n
main::CODE(0x83e47a0)(/usr/local/lib/gimp/2.0/plug-ins/dots:40):
40:         $xoffset = $xoffset % $xspacing;
  DB<2> n
main::CODE(0x83e47a0)(/usr/local/lib/gimp/2.0/plug-ins/dots:42):
42:         $img->undo_group_start;
  DB<2> n
gimp_image_undo_group_start(
        IMAGE image=1   "The ID of the image in which to open an undo group"
        ) = (
        )
main::CODE(0x83e47a0)(/usr/local/lib/gimp/2.0/plug-ins/dots:45):
45:         @bounds = $img->selection_bounds;
  DB<2> n
gimp_selection_bounds(
        IMAGE image=1   "The image"
        ) = (
        INT32 non-empty=0       "True if there is a selection"
        INT32 x1=0      "x coordinate of upper left corner of selection bounds"
        INT32 y1=0      "y coordinate of upper left corner of selection bounds"
        INT32 x2=377    "x coordinate of lower right corner of selection bounds"
        INT32 y2=233    "y coordinate of lower right corner of selection bounds"
        )
main::CODE(0x83e47a0)(/usr/local/lib/gimp/2.0/plug-ins/dots:46):
46:         if (!$bounds[0])
47:           {
  DB<2> n
main::CODE(0x83e47a0)(/usr/local/lib/gimp/2.0/plug-ins/dots:48):
48:              $img->selection_all;
  DB<2> n
gimp_selection_all(
        IMAGE image=1   "The image"
        ) = (
        )
main::CODE(0x83e47a0)(/usr/local/lib/gimp/2.0/plug-ins/dots:49):
49:              $has_noselection=1;
  DB<2> n
main::CODE(0x83e47a0)(/usr/local/lib/gimp/2.0/plug-ins/dots:51):
51:         $selchannel = $img->selection_save;
  DB<2> n
gimp_selection_save(
        IMAGE image=1   "The image"
        ) = (
        CHANNEL channel=3       "The new channel"
        )
main::CODE(0x83e47a0)(/usr/local/lib/gimp/2.0/plug-ins/dots:54):
54:         $img->selection_none;
  DB<2> n
gimp_selection_none(
        IMAGE image=1   "The image"
        ) = (
        )
main::CODE(0x83e47a0)(/usr/local/lib/gimp/2.0/plug-ins/dots:66):
66:           }
  DB<2> n
main::CODE(0x83e47a0)(/usr/local/lib/gimp/2.0/plug-ins/dots:55):
55:         for ($x=$xoffset-$xspacing;
56:              $x<$img->width+$size+$xspacing;
57:              $x+=$xspacing)
58:           {
  DB<2> n
gimp_image_width(
        IMAGE image=1   "The image"
        ) = (
        INT32 width=377 "The image's width"
        )
main::CODE(0x83e47a0)(/usr/local/lib/gimp/2.0/plug-ins/dots:65):
65:                }
  DB<2> n
main::CODE(0x83e47a0)(/usr/local/lib/gimp/2.0/plug-ins/dots:59):
59:              for ($y=$yoffset-$yspacing;
60:                   $y<$img->height+$size+$yspacing;
61:                   $y+=$yspacing)
62:                {
  DB<2> n
gimp_image_height(
        IMAGE image=1   "The image"
        ) = (
        INT32 height=233        "The image's height"
        )
main::CODE(0x83e47a0)(/usr/local/lib/gimp/2.0/plug-ins/dots:63):
63:                  $img->ellipse_select($x-0.5*$size,$y-0.5*$size,
64:                                       $size,$size,CHANNEL_OP_ADD,1,0,0.0);
  DB<2> n
gimp_ellipse_select(
        IMAGE image=1   "The image"
        FLOAT x=-19.000000      "x coordinate of upper-left corner of ellipse
bounding box"
        FLOAT y=-13.000000      "y coordinate of upper-left corner of ellipse
bounding box"
        FLOAT width=10.000000   "The width of the ellipse: 0 < width"
        FLOAT height=10.000000  "The height of the ellipse: 0 < height"
        INT32 operation=0       "The selection operation: { GIMP_CHANNEL_OP_ADD
(0), GIMP_CHANNEL_OP_SUBTRACT (1), GIMP_CHANNEL_OP_REPLACE (2),
GIMP_CHANNEL_OP_INTERSECT (3) }"
        INT32 antialias=1       "Antialiasing (TRUE or FALSE)"
        INT32 feather=0 "Feather option for selections"
        FLOAT feather-radius=0.000000   "Radius for feather operation"
        ) = (
        )
gimp_image_height(
        IMAGE image=1   "The image"
        ) = (
        INT32 height=233        "The image's height"
        )
main::CODE(0x83e47a0)(/usr/local/lib/gimp/2.0/plug-ins/dots:63):
63:                  $img->ellipse_select($x-0.5*$size,$y-0.5*$size,
64:                                       $size,$size,CHANNEL_OP_ADD,1,0,0.0);
  DB<2> n
gimp_ellipse_select(
        IMAGE image=1   "The image"
        FLOAT x=-19.000000      "x coordinate of upper-left corner of ellipse
bounding box"
        FLOAT y=3.000000        "y coordinate of upper-left corner of ellipse
bounding box"
        FLOAT width=10.000000   "The width of the ellipse: 0 < width"
        FLOAT height=10.000000  "The height of the ellipse: 0 < height"
        INT32 operation=0       "The selection operation: { GIMP_CHANNEL_OP_ADD
(0), GIMP_CHANNEL_OP_SUBTRACT (1), GIMP_CHANNEL_OP_REPLACE (2),
GIMP_CHANNEL_OP_INTERSECT (3) }"
        INT32 antialias=1       "Antialiasing (TRUE or FALSE)"
        INT32 feather=0 "Feather option for selections"
        FLOAT feather-radius=0.000000   "Radius for feather operation"
        ) =
(gimp-2.3:19817): Gimp-Base-CRITICAL **: tile_manager_new: assertion
`toplevel_width > 0' failed

(gimp-2.3:19817): Gimp-Base-CRITICAL **: tile_manager_bpp: assertion `tm !=
NULL' failed

(gimp-2.3:19817): Gimp-Base-CRITICAL **: tile_manager_get_memsize: assertion `tm
!= NULL' failed
(
        )


I don't see anything that immediately would tell me what triggers it.  The end
result seems to be correct.  I may dig into this further, but wanted it recorded
in case I don't.