OK, confirmed.
FlashGot 1.3.1
Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US; rv:1.9.1.11) Gecko/20100701 SeaMonkey/2.0.6
= NO FlashGot Media
FlashGot 1.3.0.6
Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US; rv:1.9.1.11) Gecko/20100701 SeaMonkey/2.0.6
= FlashGot Media
flashgot.media.forceCacheAsFile setting made no difference.
Nothing to note in Error Console that I saw?
A change when you reimplemented the Cache? Current browsers & older browsers certainly had different /cache/ layouts.
Again the last of the SeaMonkey 2.0, 2.0.15pre series was unaffected by the FlashGot version.
Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US; rv:1.9.1.20pre) Gecko/20110606 SeaMonkey/2.0.15pre
An old Fox, from the same era is similarly affected.
Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US; rv:1.9.2.7) Gecko/20100713 Firefox/3.6.7
(There are older FF's noted above.)
Looks to be a bunch of Luddites around. (Er, I've been known to be called that myself

.)
Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.1.19) Gecko/20110420 SeaMonkey/2.0.14 Pinball NoScript FlashGot AdblockPlus