What did you expect if you are only render QLabel! It doesn't have a parent it is not shown so it cant interact with any input. You have just created it and then you are using for painting. In fact you have big memory leak (small but frequent).
What is you real initial problem? Currently you come up with some crappy solution of some mysterious problem and you are asking us to make it work.

I suspect that you are doing something with some table view. WHAT?