Multiple Cura instances dragging down performance, can this be stopped?

[SilverDynamic 1]

Occasionally when attempting to drag and drop STL's into Cura it decides to open each one individually. It also does this when selecting STL's in a folder even if I'm just moving them around, I guess it sometimes detects a poorly timed mouse click (or release and decides) that I wanted to open all of them in separate instances.

Predictably this causes the whole Cura application to grind to a halt and I have to manually kill these instances in Task Manager.

Is there anyway to prevent Cura from opening multiple instances like this?

[ahoeben 1,968]

There is a "Use a single instance of Cura" checkbox on the General pane of the preferences.

[SilverDynamic 1]

Thanks!