Different Call Park experience with 9971

My environment:  UCM 8.5.1.10000-26

When you have a 79xx phone and 99xx phones and with both of them configured with Call Park, you will find the end user experience is quite difference.

For the old 79xx phones:

1. Phone A (7965) calls Phone B (7965)
2. Phone B answers and parks the call at 1234
3. Phone B display shows "Call Park at 1234", no light on the line button, you can make new call with Phone B using the normal method

For the new 99xx phones:
1. Phone A (7965) calls Phone B (9971)
2. Phone B answers and parks the call at 1234
3. Phone B will shows

4567
Parked on 1234

and a Resume softkey.  The indicator of the 1st session key on the right is on.
4.  You can press the Resume softkey to get back the call, as if the call is on hold.  Or you can press the 2nd session key to make new calls.  You can also retrieve the call from other phone by call in the call park number.

This is correct as per design, although the behavior is contradictory to the old 79xx phones.

Detail information in Cisco bug toolkit:
http://tools.cisco.com/Support/BugToolKit/search/getBugDetails.do?method=fetchBugDetails&bugId=CSCta34868