If anything weird happens the first thing i do is to to delete my whole build folder. Most of the time that solves the problem.

Recently I changed my pro file. I wanted to delete CONFIG += console and add CONFIG -= console. Saved it, it said it saved it, i hit build and ... it build too fast. Turns out that it didnt recompile my code, as i see from the creation time. So i had to add a whitespace, then delete it inside an cpp file to make it take my change.

Things like these cost me production time. And thats just one example of many.