Posting blinds

[JustSomeJackass]

There probably is a logical reason for this, but I have not slept much lately, so I am a little slow right now...
Why is it that when you post the Big blind out of position, it is treated as if you have called, and unless someone raises you get to see the flop for "free"...but when you post the small blind out of position it becomes dead money and you have to call the full bet to stay in the hand (instead of half a bet, like a normal small blind hand)?

JSJ

[Wingnut]

Usually when you are posting the small blind it is because you've missed your blinds and also owe a big blind. If you choose to post both at the same time, the small blind is dead, while the big blind is live. If you choose to only post the small blind (and the cardroom allows this), it will be dead, but you can play the hand as normal...you still owe a big blind after that.