Flaky performance on left rewind button

I’ve been using a Clip Sport for around four years. Recently the rewind (left) button got weird. It began toggling either the volume control or file system. Eventually it cycled back to its intended function. This drove me nuts. I assumed it was device failure after thousands of hours of use, so I found a sale on the same device and bought a new one. 

The brand new one has the same problem. I performed a firmware upgrade on the old one, so have the “new” looking file system (no improvement as far as I can see), but the problem persists on both players, old and new. 

I listen to a lot of audiobooks. If I go into the book folder and reselect a file, the left button settles down about 90% of the time, but after three to six presses, it gets flaky again. 

Since the exact same problem persists on two different devices manufactured four years apart, it’s obviously a software problem. Anyone have a clue?