Steps to reproduce:
1. load an RGB image
2. Colors>Components>Decompose (Color model: YCbCr ITU R470 256)
3. Colors>Components>Recompose

Error:  
Recompose Warning
Error scanning 'decompose-data' parasite: too few layers found

Cause:
In decompose.c, array extract[], starting at line 229:

  { "YCbCr_ITU_R470",     TRUE, 3, { N_("luma-y470"),
                                     N_("blueness-cb470"),
                                     N_("redness-cr470") }, extract_ycbcr470 },

  { "YCbCr_ITU_R709",     TRUE, 3, { N_("luma-y709"),
                                     N_("blueness-cb709"),
                                     N_("redness-cr709") }, extract_ycbcr709 },

  { "YCbCr ITU R470 256", TRUE, 3, { N_("luma-y470f"),
                                     N_("blueness-cb470f"),
                                     N_("redness-cr470f") }, extract_ycbcr470f },

  { "YCbCr ITU R709 256", TRUE, 3, { N_("luma-y709f"),
                                     N_("blueness-cb709f"),
                                     N_("redness-cr709f") }, extract_ycbcr709f }

the compose_type strings for the *256 color models have been mis-specified without underscores between the various parts of the name. 
This causes the recompose plugin to get confused when it tries to interpret the parasite.

You can see the difference on the Script-Fu Console:

> (gimp-image-get-parasite 7 "decompose-data")
(("decompose-data" 0 "source=2 type=YCbCr_ITU_R470 22 23 24 "))
> (gimp-image-get-parasite 8 "decompose-data")
(("decompose-data" 0 "source=2 type=YCbCr ITU R470 256 26 27 28 "))