Clone Stamp tool in Sampler isnt working

Trying to use the Clone Stamp tool in Substance Sampler. I can set the sample point and then click and drag over the part I wont to clone over, but nothing happens. 

In every tutorial ive watched, the area you are cloning is supposed to turn lighter, indicating the cloned texture area, but thats not happening either. 

No idea if its bugged or I'm doing something wrong, but it seems like a pretty straight forward tool, but cant get it to work.