I just switched on the MxB to test, and I could not get sequence data to be erased by using the tap tempo.
However, when I used used tap tempo the sequence end marker moved forward, the more I tapped, the further it moved until it had reached the last position. Reloading the preset and sequence and then tapping moved it straight to the last position. I had to power cycle the MxB to 'fix' this, and now it acts normally when tapping - i.e. this one is not easily repeatable (could be the sequence of actions on the first run that triggered the issue: basically selecting four or five presets and playing the sequencer while tapping the tempo, before I selected preset O5 (Rubycon) for which the tapping moved the end marker).
While talking about sequencer bugs/issues, I had the Matrix Arpeggiator corrupting the pattern several times. I think it happened when saving and/or switching sequencer modes. I've not been able to repeat that on later runs. (I was planning to report this one if/when I get a repeatable scenario)