I first noticed it on my regular MB installation.
But since that one has all the bells and whistles (plugins, virtual formulas, etc.), I used a different and clean portable install to confirm the issue.
On that one I also experienced it happening after only a few tests.
I have a slight itch that perhaps the way these installs were done plays a factor?
I used "MusicBeePortable_3_4_Update2" to install MB.
(and then I think I ran it once and closed it again)
Then I put "MusicBee_Setup_3_5_8146.exe" in the installation folder, and ran it to update to 3.5
And finally I copied the contents of "MusicBee35_Patched" to the installation folder to update to 3.5.8167