This is the first you've seen this?

Hmmmm.... I've been seeing this since OS 10.2. If you don't let your system go to sleep (I don't) it reduces the likelihood of seeing this. Anyway, if your system goes to sleep or shuts down before apps are finished with their temp files, this can happen. This is normal and something to deal with only if there's a problem. Any app can generate these files.

Google is your friend. Tons of articles and questions on support boards. Good luck understanding it — I gave up about 15 years ago.

I've been seeing it for a few years -- since Finale 2014... not prior to that, if I recall correctly.  I just finally got irritated enough to want to inquire.  I don't know which OS. 

Yes, I understand that many apps create temp files.  This is the only app that doesn't seem to be able to mange them properly if my computer goes to sleep mid-process, apparently.

You may not have heard of it before or think it applies only to Finale...

This is from 2011 and you'll notice that Finale is nowhere to be found.

https://apple.stackexchange.com/questions/17297/why-do-i-keep-getting-recovered-files-in-my-trash-after-restarting

Others blame Microsoft Office ____ (fill in the version here). iWork and many other app. You can find thousands of inquiries and endless armchair speculation on the issue plus a lot of Apple should... and Apple must or Microsoft needs to... without Finale ever coming up once. 

It's normal. Empty the Trash now and then. Otherwise, ignore it. In all my years of servicing and consulting on Macs (and Windows), I have never once seen a problem related to this issue.

Yes, I have heard of it before, and no, I don't think it applies only to Finale. However, Finale is the only application that it happens with on my computer.  

I check my Trash folder before emptying it, and I empty it multiple times per day.  I ignore the temp files.  My question had nothing to do with concern about it happening, or my worrying that it might cause problems.  My question was simply curiosity as to why it occurs, which I believe you answered in your initial response.  Thank you.

… I check my Trash folder before emptying it, and I empty it multiple times per day …

I rarely (if ever) empty my Trash folder - since I have turned the Trash into an “electronic compost” so that files are deleted from the Trash as the limit is exceeded.

Just my two cents.

I'm with Peter. Sometimes, I'll have a large file (50GB or so) and will empty the Trash to make drive space but normally, it's like ol' Ron Popeil "Set it and forget it!"

This is not an issue unless you make it one. Even then, you still won't be able to do anything about it.