Entering notes in anacrousis in a piano score removes rests in the other staff

after http://musescore.org/en/node/50121

insert note in first stave

silence diseapear in second stave,
note can't be added ,
mesure is unclickable,

Does that mean the sheet music is then corrupt ?

Do I have to do other test to know eaxctly what is the "implies" the error...?

GIT commit: 4b1e86f (from screatch)
Windows 7

Ps : major as note aren't deleted (apparently), but you ccan't have a "complete" sheet music , as silence / note aren't made