Aastra 55i call parking

If I transfer a call to 700 or use mac.cfg(softkey4 type: park softkey4 value: asterisk;7) to park the call the call is parked but when I pick the call back up at 701 it drops after 20 sec. If I use asterisk transfer (#700) the call is parked and I can pick it up on 701 and the call is not dropped after 20 sec. any suggestions?

One thing you need to do for aastra sets when conecting to aastra is set
pedantic = yes in the sip.conf general section.

It sounds like a reinvite, what does the sip trce show ?