My issue wasn't with the DDO Store key binding, but with Auto Run (which joyously binds to Button 4 on my mouse, which I never bound in DDO, which I use for PTT in Vent). Every time I would restart my client, my key bindings would list:
Code:
[ Auto Run ] Button 2 R [reset]
Which I had done intentionally, making clicking my mousewheel or pressing R do auto run. Problem was, every time I'd log back in, I'd end up with 3 keys bound to Auto Run, with Button 4 as the third, hidden bind. If I just flat out cleared Auto Run, every time I quit and come back on, Button 4 is the only one that is bound to it.
I tried messing with the key bindings like
Phiinix suggested, tried editing the keymap file directly, no go. All I could do was basically map Button 4 to a not-so-important binding. In my case, it was Loot All. No error message for pressing it while not at a chest, so it works fine for me.
Having it set as a binding to something does prevent it from resetting. If you didn't bind two keys to Loot All, you could bind Ctrl+S to "Loot All" to keep the DDO Store from rebinding on launch.
The only issue I'm left with when logging in now is it showing Button 1 mapped twice on the "Attack" binding, but that's not causing any problems.