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Could anyone help fill me in on how paying back cash advances on CCs work, and perhaps some advice on how I should move forwrad? I took one a couple months ago, and my CC billing isn't making sense to me.

Background: I got married last year. I have one credit card (BoA) with a much higher credit limit than my others, so in the run up to the wedding as expenses were piling up, I defaulted to that one, and topped out about $10k. While on the phone with BoA over another issue, I mentioned that my balance was due to wedding expenses, and the rep offered a cash advance. I normally wouldn't bother, but the offer came with a promotional APR of 0% for 18 months. I did have plenty of other costs to deal with, and it was helpful, so I took a $5k cash advance.
 
After the wedding expenses ceased, I decided on the snowball approach, paying off the smaller cards first. Thus I have not been paying much more than the min payment on this card for the last couple months. I was under the impression that the min payment would go towards my card balance (with the higher interest rate), and then anything over would go to the cash advance. However, after two months of the bills not lining up with my projections, I reviewed the allocation statement on my bill. BoA states that they 'allocate the amount of your payment equal to the Total Minimum Payment Due to the lowest APR balances first.' Excess will go to higher APR balances. This seems to have caused my snowball plan to backfire, as most of what I've paid has gone to the 0% interest account, and I'm getting a lot more interest on my balance and higher min payments, negating the whole purpose of taking the advance in the first place.

This seems wrong to me, but before I go raging into BoA, I was hoping to get some advice here. Is BoA in the right or no? Is there anything I can do to change the allocation priorities? Should I change them if I can? Maybe I switch from snowball to the other one, and just hit this CC. I'm just not sure. Any advice would be great. Thanks Reddit!
<bot>: Took promotional 0% APR cash advance while carrying a balance on a CC. Found out Min. Payment goes only to paying advance instead of interest bearing balance. Should I try to change that? If so, how?