Drive free space question

I wanted to see roughly how large a recording was. I checked the free space, and it said 841GB available. I then deleted the one show, and it said 838GB available. Why did my free space go DOWN? Shouldn’t it go up? After deleting another show, it went back to 841GB.

Does it delete files immediately, or does it wait until later to do some cleanup?

This is on a 2-tuner HDMI.