The keybindings are stored in the Steam Cloud and locally in Steam\userdata\[userid]\4920\remote\options.xml. You could try disabling the cloud support and then deleting that file (will reset all of your settings). Or just open it in an editor and see if there's something weird going on.
The relevant lines are:
<RequestHealth>Q</RequestHealth>
<RequestAmmo>Z</RequestAmmo>
<Q>Q</Q>
<Z>Z</Z>
Or you could always try the cache verification in Steam.
Comments
The relevant lines are:
<RequestHealth>Q</RequestHealth>
<RequestAmmo>Z</RequestAmmo>
<Q>Q</Q>
<Z>Z</Z>
Or you could always try the cache verification in Steam.