I was trying to record 64 steps using a single REC TRG on the beginning of a 64/64 1x pattern.
Despite RLEN was set on 64, the recorder was recording just 32 steps, then it stops recording on the middle of the pattern, then starting again each time the pattern restarted.
Just after I did set RLEN to 63 then back to 64 the recorder started to work as expected.
Any idea about what could be causing this?
Sorry, no idea. never saw this on my ot. can you replicate it? if yes, I would call it a bug. if no, I would call it “mystery” 
Let’s call it a mystery for now 
I had a similar issue yesterday, except for the fact that I am trying to record 16 steps or whatever and after stopping playback and starting again the recorders want to keep rolling for the maximum length. Also I want to sample the corresponding tracks but the OT samples inputs AB for all the four or so recorders. Tweaking the respective parameters sets them right like in the original poster’s case.
i had a weird issue yesterday when sampling my airbase. i had each midi track sequencing a different drum sound and wanted to sample each drum part separately to apply different effects/eqs… anyway, i muted the midi tracks i didnt want but as soon as i set up the recorder the muted midi tracks would play triggering the airbase. i just reset up the recorder a couple of times until it kept the parts muted. very weird…