From what I experienced today, it is possible to top up Crysta even if your UltimatePoint balance is 0 as long as you got the money in MolPoint account.

Just click top top with UltimatePay as usual and click the MolPoint tab. For those who are worried like: "Hey, if I keep converting molpoint > Ultimatepoint > crysta, won't I have balance in all the accounts and wasting money?", don't worry much.

If your UlpimatePoint account got not enough balance, SE actually allows you to pay the rest purely in MolPoint (At least that's what happened to me =O).