I was at one of UA CTO's to issue my ticket, and to my surprise I was told that this could not be done.

First, the reason was that they couldn't guarantee that my reservation could be changed if I wanted to change something. I then told them that I won't need to change anything and that I have purchased this ticket through them in the past.

Then she said that they don't do it because United has to be flown on the outbound, not the inbound (I was flying 3 sectors on SQ on the outbound, and 2 sectors on UA on the inboung). I told her that the rules stipulate that you can issue this ticket as long as ONE United segment was over water.

Her third excuse was that since UA is an alternative out of my origin city, that I should be taking the UA flights rather than SQ.

I mean, if this was the first time I was travelling with UA and they knew I was never going to come back then I can understand their refusal to issue this ticket. But I always ticket and issue with them and have never had any problem doing so...

This is odd, isn't it?