Chapter calculation error
When generating chapters of the same length (it happens to me with 360s and 480s), sometimes MKVToolNix places chapter one as the last one, with a fancy time, like 5124095:34:33 instead of 1:34:33. Possibly a division error somewhere. Seems to happen randomly, probably depending upon exact duration, and (unsure) only when remuxing mkv files.
Edited by François Collard