Kyrgyzstan is part of the Eurasian Customs Union, so from the customs point of view, the DME-OSS flights are considered domestic and duty-free purchases are not allowed on those flights.

Same applies to Armenia, Belarus and Kazakhstan and any flights between them.

Glad your transit was fine.

Just to add my data point. I regularly transit DME on the SQ ARN-DME-SIN // SIN-DME-ARN flights. I've used both an Australian and an Italian passport and there are no problems with needing a transit visa. Even if I'm near the tail of the queue it doesn't take long. There's a check against manifest (I think), numerous checking of passport and BP and security. Each time I've also been provided with an invitation to the lounge. (Flying J.) It's all quite painless.

They seem to be quite thorough and last time there was quite a drama with one passenger being taken away who was trying to enter Russia without a visa. Fair enough too.

It's not a large airport with just a few shops, bars etc airside. Duty free prices on booze are pretty good.