File copy in finder results in big files in /var/private/folders

I recently moved some big files from one of my external SSDs to another an noticed a very strange phenomenon:

During copying, files were written to /private/var/folders/.../shared-pasteboard/... , and the process useractivityd was the one reading the source files and writing those files. This went on to the point where I got warnings that my system volume was running low on memory.

Some investigating showed me that this has to do with Handoff - after I disabled it, the behavior did not occur anymore.

I like to use handoff, but it is not reasonable that it tries to store gigabytes of files in some hidden folder IMO.

Has anybody else seen this?