Your second reading is correct; I needed to supply monthly bank statements for the previous year to show that the account was active. My bank was unwilling to issue most of these as I had only had 4 entries in the whole year and the account was in excess of 400K. When I was in the bank I actually called my contact at Immigration and had her talk directly to the bank to confirm. I was told that they want to see the account used even if it is only 100 - 500 baht every month. Who am I to argue when I want my visa extended, right?