Webstorm - closing project can leave blank panes open

I often have multiple webstorm projects open simultaneously; I've noticed since updating to 2017.1 that if I close a project sometimes I'm left with a blank pane with the title of one of my JS files still floating.

It can't be closed, either, the only thing I can do is exit + reload Webstorm.

MacBook Pro, OSX 10.11.6 (El Capitan).

Anyone else seeing this happen?