After updating to version 9.3 yesterday it looks like render pause no longer functions properly.
When I click on the pause button, the huge "PAUSED" text appears in the middle of the screen, but the samples keep climbing in the bottom right corner and the CPU/GPU load in Task Manager stays the same.
I set the "Pause Real-time Render after" to the minimum amount of 16 samples. With GPU Mode turned on, real time preview never stops. With CPU Mode turned on it does indeed stop at 16 samples.
This exactly mirrors the problem in render output: GPU Mode never responds to pausing, but CPU Mode does.