Working on a mod, adding a Frost Atronach to the Render Window, I hit F to make it fall.
"F" doesn't work on Creatures and NPCs (in most cases.)
Nevermind. Dirty GMSTs were making a mess. Loaded and saved it with Bloodmoon active at some point, then kept loading and saving w/o Bloodmoon.
I highly doubt that GMSTs caused your Render Window to malfunction.
And it's impossible to load an esp without Bloodmoon if the esp already has a dependency on Bloodmoon. (the CS will select it automatically, you don't even have to do it)
The glitch was likely fixed just by rebooting your CS. Glitches and freezes happen in the CS some times.
Often, I get this weird thing where a straight line extends from the cursor and spins around it as I move it. Then I click and it selects pretty much everything in the cell.
Usually caused just by pressing the mouse buttons at the same time, or accidentally pressing the wrong mouse button when moving across the cell. Happens occasionally.
Just a little hiccup.