Strange behavior of editor (selecting text, responding to mouse)

When I click in my text, my IDEA editor (Scala plugin) selects an entire document, a paragraph, a line, a character, or nothing, apparently at random. This is hugely frustrating when editing a document.

Also, when I click a menu, it will drop down and pop back up repeatedly, and sometimes select an item at random.

When debugging, pressing the button for 'step over' can step over anywhere from 0 to 4 lines of code.

Poltergeists? How to kill them?

Eric