[SDL 1.3] Graphical corruption in OpenGL renderer

I can reproduce this pretty consistently, but I’m not sure what’s causing it.

My game engine uploads a bunch of images to textures to build a tile map. They
aren’t cleared when I change maps, since tilesets tend to get reused between
maps. There’s nothing going on that ought to change the content of the
textures. But sometimes when I switch from one map to another, even if both
maps use the same tileset, some or all of the textures in that tileset get
turned all white, and the corruption continues to spread to more textures if I
switch maps any more after that.

This does not happen in the GDI or Direct3D renderers.

Has anyone noticed this before? Any idea what’s going on? I’m running SDL 1.3
under Windows 7 64 bit.