When a person speaks in tongues, do they understand what they are saying? As a follow-up to my other question: Can people speak in tongues today?, and specifically, this answer:

When a person speaks in tongues (either historically, or today), do they understand what they're saying?

And as a logical extension, I suppose if they do know what they're saying, then asking a person who has (allegedly) spoken in tongues what they said would be a test for the legitimacy of their having spoken in tongues... or no?
The most relevant passage I can find in the Bible is this:


  1 Corinthians 14:2 (ESV)
  For one who speaks in a tongue speaks not to men but to God; for no one understands him, but he utters mysteries in the Spirit.   


I'd venture a guess that if a person is "uttering mysteries in the Spirit", they don't understand what they're saying.