Odd icon--"FS" started appearing on Win Explorer Task Bar Icons

I am posting in the hopes that someone will have some inkling why I am getting this. I'm including a screenshot of most of my taskbar at the bottom of my screen. OS is Win 7 x64, on a Toshiba laptop.

For some strange reason, four out of six Windows Explorer taskbar icons are showing up with a new icon with a blue box with "FS" on it, instead of the familiar folder icon. I don't know what this could be. For example, in a one folder, I have one open subfolder that shows up with the FS symbol, and another subfolder that shows with the usual folder symbol.

Just opened a new File Explorer window, the new window's Taskbar icon has the usual folder icon on it.

I have no idea how this happened, because I did nothing to try to change the Explorer icon. All folders seem to function in the same way, and I saw no ill effects that I could tell, or any effects other than the task bar icon. I did try to do a search on this phenomenon, but I came up with nothing. It was hard to know what to search on. I tried, "FS on Windows Explorer task bar icon."

Anyone have an idea what this may be or how it could have happened?

Thanks,
Michael

Scan with https://www.malwarebytes.org/ free (doesn't hurt to start free trial of Premium) while we search a bit

What security software are you using?

Thanks for replying.

I'm not as enamoured of Malwarebytes any more, since they went all fancy and commercial. But I had installed it a few months ago, not used it since, so I just updated and did a scan, and nothing was found. I wasn't surprised, as this doesn't look to me like a malware thing. Normally, I just use MSE, and if I think something serious is going on, I prefer to download an ISO for a disk and do an external scan with something like Kaspersky.

Anyway, after restarting (and I have the Explorer windows set to all come back after restart), I found that all the ones with FS were back to the normal folder icon. And I've seen no changes yet since the restart. Go figure--but I would still like to know what that was about!

Michael