GL ERROR - @ Post render - 1285: Out of memory

After some minutes playing Minecraft, I get huge fps drops and the log-file writes something like that: (click on "output-client.log" in the attachments)

I use the unmodded clean vanilla Minecraft. No texturepacks.
I have already tested it with the lowest settings, with OptiFine and so on. Nothing helped..

What can I do? It only affects in 1.5.1

I've forced a crash while these fps drops
you can find the crash report in the attachment