Custom textures cause rapid stobe

On entering a world of mine, all the blocks, and things like torches, were very rapidly switching between their texture (note: I do use a 32x resource pack I put together) and, mostly, flat grey.

I was able to stop the strobe effect by removing the HUD.

forgot to check with the default resources, oops.

update: the same problem happens with only the default resources. just had a thought, could be caused by the world being "old"

update 2: yeah, looks like it's one of those "old world" problems.