Damn. I think you are the fourth this week.
Your ignition cylinder is dieing. At some point, it will freeze and will have to be replaced. When that does, you will have to use two keys: one for the door and the new one for the ignition. An alternative to replacement can be accomplished by converting to a push start/toggled power setup. There are instructions on how to do it in my sig. If you don't have the tools required to mount everything I also offer prewired kits for installation.
<span style='color:gray'><span style='font-family:Courier'>1995 e36 3 Series RIP
1999 e46 3 Series BURN IN HELL
2000 MR-S Roadster= Current</span></span>