I'm unsure if this is strictly a QT Creator 4.3.0 problem or a combination of that and Qt 5.9+ (I updated both as the same time).

If you're running QMake or a simple build, you used to be able to click "run" and it would queue up to run the application once its current action was done. This seems intended as the run box is the only one which isn't greyed out during this time.

After the update, this is no longer possible. Instead the compile output immediately gives off an error:

"Error while building/deploying project (kit: Desktop Qt 5.9.1 MSVC2015 32bit)

When executing step "Make"".

It doesn't however exit or affect its current task, so it's not breaking anything. But you still have to wait until everything is done until it lets you click on "run" again.

This is a very minor issue to be sure, but an annoyance after all.

edit: I also just noticed that the compile output completely stops outputting if you click on run while it's building or running qmake. The task itself however seems to run fine even without outputting anything.