Perplexed and Bewildered

Ran across something in 2 Chronicles that has me perplexed and bewildered.

2 Chronicles 18:18-22(NKJV)

18Then Micaiah said, “Therefore hear the word of the Lord: I saw the Lord sitting on His throne, and all the host of heaven standing on His right hand and His left. 

19And the Lord said, ‘Who will persuade Ahab king of Israel to go up, that he may fall at Ramoth Gilead?’ So one spoke in this manner, and another spoke in that manner. 

20Then a spirit came forward and stood before the Lord, and said, ‘I will persuade him.’ The Lord said to him, ‘In what way?’ 

21So he said, ‘I will go out and be a lying spirit in the mouth of all his prophets.’ And the Lord said, ‘You shall persuade him and also prevail; go out and do so.’ 

22Therefore look! The Lord has put a lying spirit in the mouth of these prophets of yours, and the Lord has declared disaster against you.”

First let me be very clear.  I'm not questioning God.  He's way smarter than I am.  I'm simply saying I don't get this.  This doesn't make sense to me.  What am I missing.

Here is what has me confused.  We serve a just God.  One of God's 10 commandments is "Thou shalt not lie".  I would expect a just God to follow His own commandments, wouldn't you? 

But in this case God asks for ideas on how to get Ahab to do something stupid.  A spirit tells God how he would do it.  I'm not sure what the term spirit means but because they are in Heaven talking with God I tend to think of them as angels. 
 

The spirit says something to the effect of "that's simple, I'll just lie".  Here's what I don't understand.  God says in effect "lying sounds like a great idea".  Excuse me? 

And then verse 22.  God didn't simply say "good idea spirit, go ahead and do it".  No.  Verse 22 tells us that "The Lord has put a lying spirit in the mouths…".  So God didn't just let the spirit do it.  God took an active part in making it happen.

So how is it that a just God can use lying as a tool for implementing His will when it violates His own commandment? 

That is a puzzle for me.  Whenever I run into a situation like this I remember a quote from Ayn Rand (and yes I get the irony). 
 

Contradictions do not exist. Whenever you think you are facing a contradiction, check your premises. You will find that one of them is wrong.

I will be prayerfully considering what I am missing.  I have a hunch but I'm not sure I am comfortable discussing it yet.  Let me know if any of you out there have any ideas?

Thanks!