I use the minus key to try and stretch the number of bars in the midi editor, what happens is that what ever is in the editor at that time is repeated several times on the track I am editing.
Very frustrating because I have to delete 10 or 20 bars of repeated music I dont want!
Im using Samplitude - can't you just use the mouse to stretch it.
Otherwise I right click on the object (the bars in the track) > choose object editor. Here you can choose the length of the object - again I'm using samplitude :-)