Resolving duplicate cookie error log messages in Apache 2.4

Running Apache 2.4.7, our error logs are cluttered with messages like:

 [core:error] ... AH00011: ap_cookie: client submitted cookie 'PHPSESSID' more than once: ...

We haven't been able to determine any specific failure in behavior due to this, but also have not had success duplicating it.

Is this something we could be causing with our application configuration? If so, is there a preventative measure we could be taking to eliminate it?

Or, is it not worrisome, and if so, how would we prevent these messages from cluttering the log? (I am guessing it is worrisome, but just in case...)