So, i have seen this "bug" as well. I believe I can reproduce part of it if I
1) Create a buy order for one outcome
2) Create a second buy order for a different outcome before the first order is published to the block-chain
a) This creates a condition where the second order has a cost associated with the cost of the outcome before "1" occurs(which would move the cost now of outcome 2)
b) I wonder if because the contract told you the price of "2" but that price would have changed if executed and since it cannot honor the price declared, it simply does not execute.
c) I wonder if "2" attempts to execute before "1" or in the same block as "1" then it creates some sort of collision as one or the other would need to change the price for buying the option
On a side note I have noticed that sometimes this bug relates to the site saying it cant load the wallet please re-load. This occurred outside the condition listed above(so these may or may not be linked). I tried purchasing 10 shares (ya I am a high roller) for all outcomes on one of the dem primary races and then selling the all others. The sell command would not go through for the 10 shares each time i tried the site would say the wallet cannot load, however, I was able to sell it in two blocks of 5...which was odd.
I can tinker some more if you like and properly document this bug over the next few markets if i see it emerge again.