When UltraEdit opens a file it keeps it's whole file info (long file name, file date, file time, file attributes, short file name, ...) of the file in memory. If anything in the file info changes and it was not done by UltraEdit itself, it knows that another program has changed the file.
If the file is deleted and next a new one with the same name is created, it is not the file anymore that UltraEdit has opened (for example short name could be different). Therefore if you are working with temp files as you do, UltraEdit asks you if you wish to keep the file content of the deleted file because UltraEdit has a copy of it - the temp file. But it is just a temp file, so you need to save it using Save As command. Then Revert to Saved will work again.
If you want to reload a file which was temporarily deleted and UltraEdit has recognized this deletion and therefore handles the file as deleted even if a new file with the same name was created next, you have to close and re-open the temporarily deleted file. If you need this often you can use a macro for that job with a hot key for fast execution: