prenotes much too long

What is a prenote? A grace note? Which type, acciaccatura (the one with a slash through the stem) or appoggiatura?

I'm guessing you are referring to grace notes. And furthermore, I'm guessing you are using an appoggiatura (without slash through stem) when you actually mean an acciaccatura (slash through stem). Acciaccaturas are, by definition always short. But the correct interpretation of an appoggiatura is to take exactly half the length of the main note. So an appoggiatura attached to a half note takes one full beat. That's probably what you have done.

FWIW, this hasn't changed between 2.1 and 2.2, nor did it change between 2.0 and 2.1, nor even did it change between 1600 and 2000 :-), except that indeed, there have been publishers who have used the appoggiatura symbol where more correct practice would call for the acciaccatura symbol, especially since true appoggiaturas more or less stopped being notated as such a couple hundred years ago.