New symptom: Positions within a kdenlive project's timeline and a clip's effects and transitions weren't synchronized.
Same solution: $ mv ~/.config/kdenliverc tmp worked again! That's the good news. The bad news? The aptly named "debugger" (gdb) fixes [mlt_pool] out of memory Not by finding the bug. It just stops it from happening. So far. So, Kingsley -- Time is the fire in which we all burn.