handling of existing note when changing time signature

This is observed in both 0.9.4 and r1723 on XP and Vista.

Not really sure if this is a bug or I just have the wrong expectation. Here's the situation:

Say you already have a musical passage in 4/4 time. Now if you change the time signature to 2/4, what should happen?

My expectation is that the passage would now be notated into twice as many measures but otherwise remain intact. What actually happens is that the notes in the last two beats of every measure simply get chopped off. I think this is probably not what most people would have wanted.