I've been running into numerous crashes when deleting jit.pwindows while a complex GL rendering process is running. The pwindows doesn't have to be part of that rendering context. Closing an unassociated help patch with a pwindow while the rendering patch is running triggers it as well.
On one machine (hackintosh OSX 10.7.4, i7-2600k, Radeon HD6870) I get errors before the crash:
jit.gl.fbo: error initializing capture
jit.gl.fbo: unsupported framebuffer format!
(repeated a bunch of times)
On my genuine Macbookpro (OSX 10.7.4, core2duo, Radeon X1600) I don't get the errors but the whole system freezes. Or becomes really sluggish, as in a window appears minutes after a click.
Both run Max 6.0.7.
The patch below demonstrates. Delete the marked pwindow while qmetro is running. After 20 seconds or so Max will crash.