This bug is very similar to http://community.qnx.com/sf/discussion/do/listPosts/projects.graphics/discussion.
advanced_graphics.topc6683 and maybe caused by the same code.

OpenGL ES 1.0 specification concerning eglChooseConfig() function says (small example):
EGL_RED_SIZE
Must be followed by a nonnegative minimum size specification. If this value
is zero, the smallest available red buffer is preferred. Otherwise, the largest
available red buffer of at least the minimum size is preferred. The default
value is 0.

The same for BLUE and GREEN and ALPHA.

Default photon video mode is set 640x480 32bpp. I set EGL_RED_SIZE, EGL_GREEN_SIZE, EGL_BLUE_SIZE to 5, 5, 5 and ALPHA 
to EGL_DONT_CARE, but eglChooseConfig() always selects 8,8,8,8 framebuffer configuration, while 5,5,5,1 and 5,6,5,0 
framebuffer configurations are available.

When default photon video is set to 640x480 15bpp (RGBA5551), eglChooseConfig() chooses 5,5,5,1 mode as requested.

This bug can be reproduced in my case using at least devg-tnt and devg-radeon video drivers.