"Go to slot..." in design mode: "No documents matching 'ui_mainwindow.h' could be found"

1. Create a GUI project.
2. In the *.ui file displayed in the Design mode, click "Go to slot..." from the context menu of the form and select a signal.
3. The error: "No documents matching 'ui_mainwindow.h' could be found.
   Rebuilding the project might help." is displayed in a pop up.

This is a regression from 2.7.