Question: why glXMakeCurrent() with a None context leads a dead lock on some platforms?

[Wohlstand]

During my experiments on Mac OS X Tiger, I accidentally found that that attempt to make the None context current, leads to a deadlock. So, I disabled that block on my side. However, I want to get an understanding of why it happens. Is that a bug of certain X11 implementations? At my end, there is a very old X11R6 based on XFree86. The same code works fine everywhere, it gets a deadlock exclusively on the Mac OS X Tiger's X11.