FYI - Just had a look in my temp folder and there seems to be a new razor folder roughly every day. Among the files inside is always a cs file that appears to be from the Revindex task scheduler as it contains the code from the task that I have on the server for Xero updates. I have that running once per day, so that fits.
Each of the folders has it's own unique name e..g. RazorEngine_5k3op2gq.icw
So yes, I can confirm I'm also seeing folders there, and if the task ran more frequently or on more portals, then there'd also be more folders.
It's certainly not cleaning up after itself.