Dual Sim Phones and Premium Numbers?

Can I ask anyone using a Dual Sim phone with 2 Sims in it to do a test for me?

I have a OnePlus X and have 2 Sims in it, but if I dial a 'Premium' number (like ones starting 0844, 0800, etc) it always uses the preferred Sim (Sim 1 for me) to make the call.

If I dial using the dial pad and chose to call using Sim 2, it dials with Sim 1. I've also tried saving the number in my contacts and setting the phone to always ask which number to use. When I press it I get asked which number to use, I select 2, and it dials using Sim 1.

I've got no issue dialing 'normal' numbers using Sim 2, or receiving calls on it.

If I swap the Sims around or set Sim 2 as my preferred, it will keep always using the preferred one for these numbers no matter what, so its not any restriction on the network, it seems to be something in the phone causing it to use preferred Sim only for Premium numbers?

Has anyone got a dual sim phone that can't test if you get the same behaviour?

I can try, although mine is a Windows 10 Dual SIM phone so the behaviour may well be different anyway.

Edit: Works fine.

I've moved to CyanogenMod on my OPX and the behaviour has gone. So it looks like an issue with the stock OxygenOS on the phone.