Each time Rufus 4.2 is started, RufXXXX.tmp (language messages, >1M) is created in app directory and not deleted once Rufus is closed.
Also reproducible with original rufus-4.2p.exe file, without PortableApps environment. Definitely a Rufus bug, not a PortableApps one.
So, if Rufus 4.2 is started N times, then N+ megabytes is occupied in Rufus app directory.
Not reproducible with Rufus 4.1 or older.
Update #1. This bug occurs because I use a RAM disk R: (ImDisk ToolKit) and my TEMP and TMP are R:\Temp (no symlinks). In this case Rufus 4.2 creates temporary files in . directory for unknown reason and just forgets to delete them. Looks like the bug is introduced here: https://github.com/pbatard/rufus/compare/beb847511bf75c4120a3a5b23e0785b...
Rufus 4.1 worked correctly. That is, temp. file is created in R:\Temp and deleted before Rufus 4.1 is closed.