timer-idle-list
working emacs:
([nil 0 0 500000 t jit-lock-context-fontify nil idle 0])
broken emacs:
([nil 0 0 500000 t jit-lock-context-fontify nil idle 0] [nil 0 0 500000 0.5 blink-cursor-start nil idle 0])
Although calling cancel-timer on the timers does not fix the problem,
I have also noticed that, with toggle-debug-on-quit on, just typing C-g while in the normal writing buffer will always send me to the debugger on only one line:
Debugger entered--Lisp error: (quit)
internal-timer-start-idle()
This happens in the broken emacs only, and C-g here does nothing in the working emacs. Likewise, in the broken emacs, while I am highlighting text with C-space, C-g will 50% of the time cancel the highlight and 50% of the time open the above debugger on the timer start function. In the working emacs, of course, it cancels the highlight 100% of the time.