4.3 adds a beat to a measure, without my asking it to . . .

I just installed 4.3. Right off the bat it’s doing funny stuff: in a simple 4 part score in 3/4, when I get to measure 5 and add an eight note pitch to the bar, the bar becomes a 4/4 bar with the dreaded + sign in gray at the end of each staff. Deleting that measure, and the measure before and after does not stop this behavior.

[I am adding notes as I always have, note value with the keyboard like 4 for eight notes, 5 for quarter notes, and note pitches also via keyboard (I am careful to not have 'it' decide to enter a pitch from the movement of the cursor - which I sure wish I could turn off — but that another issue). Here, I enter the first 4 measures just fine, then measure 5 this strange behavior starts. I can enter 8th note values in all four parts, just as eighth rests, no problem. But as soon as I enter a note pitch to any eighth note, ‘It’ turns all the measures #5 into 4/4, with that dreaded greyed + sign at the end of all measures #5. What am I missing ???