Looks like, to my great dismay, the touchpad is once again helfully reacting to taps as button clicks.
I forgot what I did, a very long time ago, to turn off this "helpful feature" in the first place.
But, looks like after upgrading to F29, at least on the XFCE desktop the phantom clicks from the touchpad are BACK once again. I am positive that this is new to F29. Perhaps this used to be configurable in settings, somewhere, but the support has been removed for some reason. I find nothing promising in "Mouse and Touchpad" settings, now. Checked accessibility. Nope. Can't think of any other place to check. Where, oh where, do I get rid of this, once and for all?
I found some old stuff in Google for Fedora 20. Looks like it might still work. I dropped the following into /etc/X11/xorg.conf.d/10-disable-taps-once- and-for-eternity.conf:
Section "InputClass" Identifier "tap-by-default" MatchIsTouchpad "on" Option "TapButton1" "0" EndSection
Crossing my fingers that this works. So far, intentional double-taps no longer appear to elicit a response, so I'm optimistic.
Still, why did this harassment start back up again, in F29? I really don't want to remember to do this manual hack again, if I ever install Fedora on a new laptop.