Confusion when changing Time Signature

1) New Piano score>4:4 with 1/4 Pick-Up
2) Change Time Signature to 3:4
3) Change Measures of first bar to 1/4 Pick-Up
4) Enter notes into second bar: You get four crotchets, instead of three.

I had a similar error where it would only allow me to insert one crotchet per bar. When trying to replicate the error, I encountered this. If I manage to replicate the initial error, I'll post it - perhaps the team here will even find it!