[mark_k]

Thanks. I ran the TestBild program selecting various modes and that showed up some issues.

4 bit mixed 320x200: Image half width. (Appears correct size with 8 bit packed color mode.)
4 bit mixed 1600x1200: Bottom of the image is corrupted, looks like there is some kind of wraparound? Same happens with 8 bit packed 1600x1200.

15 bit Targa 160x120: Two half-width images appear size by side
15 bit Targa 160x240: Two quarter-width images appear side by side
15 bit Targa 320x512: Image half width

16 bit XGA 160x120: Image appears correct (contrast with 15 bit Targa 160x120)
16 bit XGA 160x240: Image half width
16 bit XGA 320x512: Image half width