Call transfers involuntarily between extensions

Hi,

We just wen live with an Asterisk/Elastix installation last week.

We are noticing that some calls are being transferred between extensions involuntarily. The caller would be in the middle of a call and then the ring on another phone and transfer without hanging up.

This does not happen all the time, so far it seems kind of random.

We are running Elastix 1.5.2-2 with Aastra phones.

Any idea of why this might happen? Where should we look for a solution?

Thanks,

Eduardo