Comment 4 for bug 1404900

I've got the same problem on two linux desktops (QtCreator 3.2.1).
You just need to hold Ctrl and move the mouse over some code. For every function, variable or class, QtCreator will try to find where it is declared (has to do with the Ctrl+click shortcut to "Follow Symbol Under Cursor", Ctrl without click will already underline variables/functions and turn them blue if QtCreator can find where it is declared). For any reasonably large project, this takes too much time, especially when the declaration is "far away", e.g. in some other project. You have to take great care not to have your mouse cursor over code when using any keyboard shortcut that includes Ctrl.
This bug pretty much broke QtCreator for me...