Mac standalone renders different in different resolutions

I've got a project where if I play in 1680x1050 as a Mac Standalone - or in the editor - it renders fine but if I play standalone in 1600x1000 almost none of my transparent stuff renders. Has anyone seen this or know what's up with it?

EDIT: I've narrowed this down to only happening when I use Water 4 and some kind of image effect, together, and it seems the native res on the monitor always works. I wouldn't be surprised if there's just not enough VRAM to go around when the game's not in native res...?