Explorer Folder/File Handle Leak? (USB Eject)

I am experiencing a problem regarding ejecting USB devices that may indicate a more fundamental issue with Windows/Explorer within Windows 10.

In the last one to two weeks (possible updates?) it has become increasingly difficult to eject USB devices.

Process Explorer handle search reveals Explorer is keeping open directory handles and thus preventing the ejection of the USB devices. Killing Explorer (or deleting the handles) permits ejection (obviously).

A slightly deeper look into this reveals that browsing to a specific directory will result in handles being opened for all sub-directories. Moving away from that directory and/or closing Explorer does not close those handles, and thus prevents any removable media from being removed "safely".

One of the possible problems is Context Menu hooks, so I've disabled all of those as a precaution but the problem continues.

Is anybody aware of any problems and associated solutions?

As an aside I looked on the Microsoft community forums, with a view to posting there, and commentary around this kind of issue is being directed toward TechNet.

EDIT: Digging a little deeper I was able to remove a lot more shell extensions and alleviate the mass folder handle leak. So Explorer is not the issue. When I get more time I will trawl the extensions to look for the culprit(s) and report back. Nothing out of the ordinary was extending; Dropbox, Notepad++ and a few other well used/known products, but nevertheless one or more of them is causing issues.

The problem persisted with system still holding handles to the classic $extend\$rmmetadata. Process Explorer was unable to close the handles (in admin mode).

Removing the drive letter in Disk Management released the drive I was testing with, and switching off indexing on the drive appears to resolve the issue for now. Will do more testing and report back.

If anybody else has information on this matter it will be much appreciated.