Well, I didn't end up doing any complex capture of my rendering process, due to time constraints. I just did a regular git bisect. I found that my linux problem is caused by commit c0e01d9cd71bd958e1b31a03cea4c08a1bdf4926 ([xlib] Improve GC caching efficacy) I haven't dug in past that -- is that enough for you to go on? Unfortunately this undoubtedly disproves my theory (hope?) that I was seeing the same problem on Linux and Windows. So I guess tomorrow I start on that bisect. Damian