Because of your entry, I looked at my iPhone reminders and found the same thing: a SIRI created task was listed below the RTM default list.

I went to Settings>Reminders and opened/closed both sections [Sync and Default List] without changing their values. This caused a reset of some sort as my task immediately moved to RTM.

I then used SIRI to create another task and the process worked correctly.

I just tried that and it help in my case.

I meant to say it did not help in my case.

Although my tasks were going to RTM a copy was still in the Reminders app. So, I decided to start from scratch.

I deleted the calDAV account we had originally created. Went to Settings>Reminders and found the default list still said RTM. I rebooted the phone and the default list had correctly reverted to "Reminders".

I set it up again. The task pushed to RTM. It still shows in Reminders so I'm right back where I started.

Did you figure it out?

No, mine isn't working at all.