fliphorz=flip_horiz.svg
flipvert=flip_vert.svg
Pasted these two images into another random folder to work on them
Renamed the files - swapped filenames
Cut/Pasted the edited files back into source directory
Reopened ImageGlass
They now function as expected based on the icon.
Previously, the horizontal icon flipped the image
vertically and the vertical icon flipped the image
horizontally.