On some occasions more than one write-back required to clear flag

[greg]

I've noticed that on some occasions more than one write-back is required to clear the write-back flag. Recently I have changed groups of files adding one keyword and deleting another. Two write-backs are almost always required. Upon testing it looks like just deleting a keyword requires two write-back events.  Note that this is going to a NAS drive, though that might not matter. While this isn't a critical issue it can be annoying when many files are involved.

[Mario]

This is normal.

It can happen if the metadata contained in the file (legacy IPTC, EXIF, GPS) is not synchronized properly and IMatch has to deal with metadata mess.
IMatch may need two write-backs to synchronize the data, usually keywords.

This mostly depends on the state of metadata in your files, which software / tools you have used to modify the metadata etc.