Yes, there is really a bug in the panel plugin. I am of half a mind that the bug is the fact that it exists.
Indeed. I just tested, and indeed, the REAL bug is the fact that even if you DO DO the RIGHT things, it STILL scolds you. That is, you insert a USB device. You then use the "ejecter" panel thingie to eject it, you get the message that it is now safe to remove it. You remove it, and then it scolds you for not ejecting it before removing it.
My overall sense here is that whoever developed this didn't think it through very well. They didn't really analyze to figure out if it was necessary or not; they just followed MS's lead. I.e., it would take a lot of real thinking and planning - thinking about all the possible things users could do - in order to determine if this is needed functionality or not. It is much easier to just say "Well, MS must have done all that thinking and planning; they concluded it was necessary, so so should I".
Also note: Given that most removable devices (i.e., the kind that can and should be "hot-swapped" - on the Pi, this excludes normal hard disks, since the Pi has no facility for an "internal" hard disk) are formatted with some kind of FAT filesystem - and the whole point of FAT is to be "what you see is what you get" in terms of caching - i.e., it pretty much is always safe to just pull it, well, maybe this whole effort (to prevent users from doing this thing) is all pretty much moot and much ado about nothing.
Nitpickers note: In the previous paragraph, I said "most". I'm well aware that many of you may have removable devices formatted with other-than-FAT type filesystems. That's, however, beside the point.
And just to be even more explicit, the point of the "new" exFAT filesystem is to retain the "what you see is what you get" semantics of FAT while supporting large media. FWIW, when exFAT first came out, I was really confused; I didn't see what the point was since NTFS seems to do everything that exFAT was doing. But then I realized that the point is that NTFS is not "hot-swappable"; the point of exFAT was to be hot-swappable.
And that's all I have to say on that...