Middle mouse paste not working reliably


I'm using FreeBSD 11 with KDE. I've noticed that copy/paste with the middle mouse button is intermittent. It tends to work once (and even then only after a long click) and then tends to stop working completely. It's a wired Logitech mouse with a scroll wheel that can click down, left and right.

I've tried running 'xev', and I see events for everything (mouse move, left and right buttons, middle button scroll down and up, middle button click left and right but _not_ middle button click down).

Any ideas what the problem might be?

Perhaps an issue with the mouse, I'm trying another one and it seems to be working much better.