Determine extension to use for outgoing calls


First of all, I’m not sure if this issue is related to the PBX or the phones but i’ll explain my problem:

We use Linksys SPA942 and SPA504g phones and we have placed two extensions on 1 phone. Extension 1 is the regular extension to receive calls from queue and extension 2 only receives emergency calls (thats is why we made a seperate extension for this).

When a user makes an outgoing call this sometimes takes place from extension 1 but other times it takes place from extension 2. I cannot explain this behaviour but I noticed it in the CDR.

I want extension 2 to be available as much as possible and outgoing calls should allways be made through extension 1. Anyone any suggestions on how to fix this?

Thanks in advance,