LW decides for itself whether it needs you to be an Ultrapeer or Shielded leaf. One doesn't have an advantage over the other. The network is very dynamic and changes from one second to the next. So one time you might connect as an UP and next time as a leaf. I think it's normal, I've had it do the same thing.
Here's a couple threads with more info:
What are peers and ultrapeers & leafs?!?! Peer, Ultrapeer, leaves... ?? Someone explain !
Also searching the forums is a very useful way to find answers to your questions. The search button is in the upper right of this page between f.a.q. and home
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