Issue saving file on :w

When using the 4.15.0-* versions of Qt creator it sometimes become impossible to save a file using :w. It just displays a message indicating that the file could not be saved in red background in the command box on the bottom right of the screen.

Saving by right-clicking on the file name and save in the opened file list works though.

I don't know how to reproduce it, it happens quite randomly and when happening the only way I found to stop the issue is to restart Qt creator.

Seems similar to QTCREATORBUG-12810