I've compared CHDK & Free mem size for two cameras: sx130 and a495 (trunk958 with my changes, there aren't any images on disk):
sx130: CHDK - 260064, free - 206969;
a495: CHDK - 266480, free - 203544.
Free mem size for both cams is the same but a495 hasen't any problems with low memory.
From dump:
heap start: sx130 - 0x166210, a495 - 0x128e90.
DRY HEAP END: sx130 - 0x2f1f80, a495 - 0x2724a8.
So, heap size: sx130 - 0x18bd70, a495 - 0x149618.
Heap size sx130 is more then this one for a495!
Free mem for sx130 after shoot in PB mode is about 40 kb. Perhaps, image is placed into heap? a495 has 200 kb free memory before and after shoot.