Simple VBA stuck on "running"

I have a simple userform (FilterControls) with a button (Message). The button only has one line of code: MsgBox "You clicked the button.", vbOKOnly, "Congrats!"

I have a second button (Show Form) on the worksheet (nothing else in the worksheet) set to run a single line of code: FilterControls.Show

1. I click the Show Form button, and it shows. In the Visual Basic Editor window, I can see the "[running]" indicator at the top of the window.
2. I click the Message button, and the message appears. I can still see "[running]" in the VBE window.\
3. I click the OK button in the messagebox. "[running]" still shows in the VBE window.

Somehow, the code isn't completing. What am I missing?