Traz is right. At this point you will have to buy into UTs each month or start another RSP that is not ABF amd MBH.
Btw, here is my theory on why this is the arrangement.
DBS earns a distributor's commission from the sale of these UTs but the maximum amount is at the time that a new folio is created, i.e. a customer buys into it for the first time. And so in order to maximize new folios, they require folks to sell in full and wait 6 months is because it is only after 6 months of zero-holding that the UT fund house counts a new purchase as a new folio.
I don't know why they count an RSP as an investment category for 12 months only. I have 2 theories: (1) in order to force people to create new folios every year, and/or (2) although DBS earns a commision each month, after 12 months this commission is pittance.
Maybe this has been discussed here already, or the answer is already out there, in which case I'll happy to be enlightened.