After installing Beta 5 through auto update, I was welcomed with the problem of some non-working child window covering the top portion of the Workspace Explorer window (as shown below):
Here is how to get rid of it:
1) Click the little thumb-tack to set it to Auto-Hide
2) From the Menu Bar, select "View" > "Workspace Explorer"
3) Click the little thumb-tack again to turn of Auto-Hide
This worked for me, if you have this problem, I hope it works for you!