Please describe the problem:
See below.

Steps to reproduce:
1. Create two panels extended to the width (or height) of the screen
2. Position these two panels along one edge of the screen
3. Launch any application with a maximizable window and maximize it.


Actual results:
The window becomes too broad/high, as if the second panel did not exist at all. If you move one of the panels to another edge now, the problem disappears: both panels are taken into account by maximized windows.

Expected results:
The window takes free screen estate without slipping under the panels.

Does this happen every time?
Yes.

Other information:
It is easiest to desribe the reason by means of xwininfo and xprop. Here is the output for the first (nearest to the right edge of my screen) panel:
$ xprop | grep STRUT
_NET_WM_STRUT_PARTIAL(CARDINAL) = 0, 28, 0, 0, 0, 0, 0, 1049, 0, 0, 0, 0
_NET_WM_STRUT(CARDINAL) = 0, 28, 0, 0
$ xwininfo          

xwininfo: Please select the window about which you
          would like information by clicking the
          mouse in that window.

xwininfo: Window id: 0x100002b "Правая расширенная краевая панель"

  Absolute upper-left X:  1652
  Absolute upper-left Y:  0
  Relative upper-left X:  1652
  Relative upper-left Y:  0
  Width: 28
  Height: 1050
  Depth: 24
  Visual Class: TrueColor
  Border width: 0
  Class: InputOutput
  Colormap: 0x20 (installed)
  Bit Gravity State: NorthWestGravity
  Window Gravity State: NorthWestGravity
  Backing Store State: NotUseful
  Save Under State: no
  Map State: IsViewable
  Override Redirect State: no
  Corners:  +1652+0  -0+0  -0-0  +1652-0
  -geometry 28x1050-0+0

$ 

And here is the output for the second panel:
$ xprop | grep STRUT
_NET_WM_STRUT_PARTIAL(CARDINAL) = 0, 28, 0, 0, 0, 0, 0, 1049, 0, 0, 0, 0
_NET_WM_STRUT(CARDINAL) = 0, 28, 0, 0
$ xwininfo 

xwininfo: Please select the window about which you
          would like information by clicking the
          mouse in that window.

xwininfo: Window id: 0x1000003 "Правая расширенная краевая панель"

  Absolute upper-left X:  1522
  Absolute upper-left Y:  0
  Relative upper-left X:  1522
  Relative upper-left Y:  0
  Width: 130
  Height: 1050
  Depth: 24
  Visual Class: TrueColor
  Border width: 0
  Class: InputOutput
  Colormap: 0x20 (installed)
  Bit Gravity State: NorthWestGravity
  Window Gravity State: NorthWestGravity
  Backing Store State: NotUseful
  Save Under State: no
  Map State: IsViewable
  Override Redirect State: no
  Corners:  +1522+0  -28+0  -28-0  +1522-0
  -geometry 130x1050-28+0

$ 

Obviously, _NET_WM_STRUT is set incorrectly (it should be 158 for the second panel).