I'm not sure if this is common but I've seen that happen on most of the older models. This does point to faulty actuator or vacuum situation on the driver's side door. However, if you started to trouble shoot that you're bound to end up with more than $100 to $200 worth in labor and parts. easiest thing to do is either to use the trunk or the pass side to lock, or you can invest in a remote lock/unlock module for around $100 and make life easy for yourself. this way you won't have to bother using the key at all. just a suggestion. atleast that's the route I took.

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