According to the wikipedia article, it looks as though Lee was more or less stuck with them as an inheritance (more of a burden than a gift), as opposed to going out of his way to acquire slaves.
Yes it does.
It presents a conundrum. According to something I read regarding the Irish Riots in New York, a Slave was worth $1,000 dollars at the time. A thousand dollars was a huge sum of money in 1860. I would suppose it might equal 20-30 thousand in today's dollars.
Supposing that even if you were against slavery, what would people be tempted to do if they inherited several slaves in that era? Well, you could throw away all that money by manumitting them, you could sell them and recover the money, but if you did so you would putting at risk how well they would be treated, or you could employ them yourself in an effort to recover some of that value.
I suppose Lee must have regarded the last possibility as the most reasonable solution to his situation.
These perverse incentives stem from the problem caused by putting a monetary value on human life in the first place. Of course the practice originated out of Muslim Africa, and is not in conflict with the Tenets of that religion.