Works here, can you give some more details?
(the second part, after I extend the left item border, is where the bug discussed in this thread used to creep in. That bug is properly fixed, as far as I can tell)
Ah, wait, maybe this helps:
As a rule of thumb, if you want to tweak MIDI loop source length in Reaper, it's best to always tweak the border of the
first (complete) loop iteration.