Treble Clef 8va Bassa—possible bug

I have version 3 of MuseScore installed on my Mac (v. 3.0.5.21343). I am writing something out for bassoon in the Treble Clef 8va Bassa (Thats the G-Clef with the little 8 underneath often used for the Tenor part in Vocal scores). I keep having notes right around the middle of the staff jump down an octave. In other words, I might write a series, B-A-G. I put in the A (A3) and, instead of being one step down, it comes out a 9th down (A2). This tendency to jump down an octave from what I expect is happening very often.

Here is an example. The first half of the measure looks fine, but then this unexpected jump occurs. This doesn't happen always, so I can't reproduce it definitively.