I just sifted through my old floppy disks, and this caught my attention. My first floppy drive was single-sided, hence the cutouts. No, this is not what I mean. This is a SSDD disk - look at the label on the upper left corner. I doubted that they actually existed.
The problem is that when you have a sector dump disk image of 180 KiB, this should be considered a DSSD disk. For the sector dumps, MAME actually peeks into sector 0 to make sure, but if that disk is not formatted, this may be a problem, because a SSDD disk with 18 sectors/track, 40 tracks, and 1 side has exactly 720 sectors like a DSSD disk with 9 sectors/track, 40 tracks, and 2 sides.