voodoo47: try to delete user.bnd in your TG folder.
Thanks for your reply, but the problem persists.
Deleting user.bnd just resets the keys to the TFix default, which oddly doesn't bind anything to 'Walk Forward', and doesn't bind 's' to anything, yet holding 's' causes you to walk forward, but at a pace slightly slower than of walking while crouched, and with the pronounced head-bob of walking crouched (but still not actually crouched).
Still can't walk up steps though. Also can't walk up steps having bound 'Walk Forward' to 's', despite being able to walk up steps with 'Walk Forward' bound to 's' before TFix. I have also found that after TFix I can't go up stairs walking backwards, or sliding left or right, whereas I can do so before installing TFix. This change happens with both default and custom key-binds.
So thanks for your suggestion, though. Do you have any other ideas?