I posted a thread in technical support a while ago regarding autorun incorrectly activating whenever I moved and then pressed TAB (bound to targeting, as per default). In preparation for Stormblood I decided to dig a bit deeper and try to figure out the cause of this and I seem to have found it.
First, to solve the issue I tried to delete my data folder within Documents/My Games/FINAL FANTASY XIV - A Realm Reborn. This solved the problem.
Then, with my old settings restored again, I tried to reset keybindings within the game. This also worked.
I proceeded to take note of all my keybindings, reset them and fill them back in, one by one. Between each entry, I tried to reproduce the bug.
Luckily, I found the problematic keybinding right away. My keybinding for, "LB Button" under the, "Gamepad" category which was set to CTRL+SHIFT+TAB seemed to be the issue.
After further investigation, I discovered that the issue appears for any keybinding set to, "LB Button" under the, "Gamepad" category. Ouch
So to reproduce the bug:
1. Keybind said shortcut, "LB Button" under the, "Gamepad" category. So far, I have not found a keybinding that does not trigger the bug.
2. Proceed to move in any direction and then click the button registered to said shortcut. Modifiers don't trigger the bug but any other key will do. E.g TAB, letters, numbers, etc. Also, unlike regular autorun you have to be in motion for the bug to occur, it will not work while standing still.
3. As you release all movement buttons, the character keeps moving, as if autorun has been enabled even though you never pressed a keybinding for autorun in the first place.
I have not tested to see if the issue occurs with any other shortcut, this is the only one I experience it with. But it happens reliably and, as mentioned, with any keyboard shortcut.
TL;DR: Any keyboard button(s) bound to, "LB Button" under the "Gamepad" category will trigger autorun when in motion