Using imcoadd with fl_over+ does not clean up the photometry FITS file used for scaling. Once the task gets past stating the scales to be used, there is a warning that
Operations would overwrite existing file (*mag.fits)
where the table in () is the name of that photometry FITS file.
The warning comes from the tcopy on line 1892 as far as I can see.
The file should have been deleted with the *_trn_mag files in the delete on line 526 when fl_over+
The bug means that the user has no merged record of the photometry used for the scaling. The scaling itself seems to be unaffected.
The bug will be fixed in a future release. Meanwhile the user can work around the bug by just deleting the *mag.fits file before rerunning imcoadd.