after making large adjustment to slur, it becomes extremely difficult to select
It's easiest to understand this bug by watching the following video (it's the second bug mentioned):
The way I caused the bug to happen was by making the slur really tall, after which it becomes nearly impossible to select with the mouse. Doing 'CTRL-A' then 'Esc' allows you to grab the slur again.
I'm using beta2 in the video, but the issue also occurs in MuseScore nightly ff2b92c on Kubuntu 14.04 64-bit.