I see a few problems here:
* Saving a file will enable the designer even is some errors were reported thru the signal onAnalyserError and not yet fixed.
* In case of file close, the file in Phobos may be different from the file handled here. In that case, the designer will be disabled while it shouldn't have been.
* I would prefer to handle the designer state only within phobos and really at project level instead of a file level.