As EsherFlyer says, MBNA changed the order of payments very recently, so some of yours may have been caught on the wrong side of that change.

The other factor may be that, because you are carrying a balance from your previous statement (albeit an interest free one), you don't get the usual interest free period on purchases - they start accruing interest from the day you charge them to the day you pay them off.

The wording on the statement is:

Another reason why the usual advice with balance transfers is to put the card away somewhere safe, and not touch it until you have paid off the transfer.