The Tap-and-Drag Gesture does not function if you have Mouse Click Emulation for One finger set to "No action". As such, it should be disabled / grayed-out when this is selected. Observed on Kubuntu 14.04 (KDE 4) and Manjaro 15.12 (KDE 5.5.1). Reproducible: Always
Hello! This bug report ticket the Synaptics version of the Touchpad page, which is no longer supported in Plasma 6. Can you please see if the issue still happens when using Libinput? Thanks!
(In reply to Nate Graham from comment #1) > Hello! This bug report ticket the Synaptics version of the Touchpad page, > which is no longer supported in Plasma 6. Can you please see if the issue > still happens when using Libinput? Thanks! Even in Plasma 5, the dialog has been completely redesigned, so this bug filed against a 10-year-old version is irrelevant.