You're right heardie. This is already covered in the readme - sort of. Since a merged FLICster file is actually a Civ3 Unit FLC (if i've done everything right), all of the info in "the gory details" section of the readme file applies to merged flcs as well as originial Civ3 Unit FLCs. Section "1 - Frames" in The Gory Details covers this behavior - the extra frame is the ring frame, which is the delta from the last true frame (10 in your example) to the first.
Incidentally, keep a watch here on CivFanatics for the next major release version of FLICster - at least another week away (sorry, I've been sick). Among many cool new features, the new version will allow you to view Civ3-style Unit flics - in original color or with alpha blending enabled ( in other words, with true shadow & transparency), from any direction. The number 1 design goal of the new FLICster is to eliminate any need for an animation program (such as AS). You will still need a graphics package (Paint Shop Pro, or any of the others).
I've let enough cats out of the bag. Back to work....