I’m sure I’ve discussed this before, but the behaviour is known (and somewhat deliberate) and is not viewed as a bug I think. As soon as the tempo varies, even a little, the os assumes a ‘new’ change and effectively blocks that undo, or possibly treats the tempo change as the last variation in the edit buffer. See if undo still works when you delete a pattern and then adjust tempo a fraction and then undo, whilst slaved to nothing!
It’s a pity that the behaviour is configured this way, but it’s been known by hq for a long time
I have sent them a ticket anyway…i would not use Bpm changes as something influencing the buffer.
I also remember (not sure anymore) that when i was first getting curious about A4, I saw somewhere that its Patterns would have been linked to Bpm…so each Pattern its own Bpm.