I saw this behavior in Linux Mint 16 Cinnamon and MATE editions, but it may affect other distros as well. The problem is that the “touch-tap” functionality wasn’t working, e.g., tapping on the touchpad to simulate a mouse click was being ignored. It turns out that this functionality just happens to be turned off by default, and there’s a simple fix:

1. Open Control Center.
2. In the Hardware section, click Mouse.
3. Go to the Touchpad tab.
4. Make sure the “Enable mouse clicks with touchpad” option is checked.