Why doesn't pressing '7' when entering a sting of 8th notes change the length to semibreve without editing?

Fairly new to Musescore and working on a big band arrt. This may be a simple mistake on my part, but when entering a string of say, 8th notes, as I go over the bar to the next bar, with a semibreve rest in it, you get another 8th note. But if I come out of note input and pres '7' to indicate I want a semibreve, back in note mode I just get a crochet again. I have to then come out of note entry, select the note and then press 7 to convert it to a semibreve. Can you note change note length as you go? What am I doing wrong? Thanks!