First of all what you have configured is not a proper shared line but a combination of shared DN and shared numbers among different DN's.

Their proprieties are quite different. In short, the first will make ring all the phones where the DN is configured on a button.

The second, will make ring only one DN/ephone at once, depending on the preference configured under ephone-DN. Because by default the preference is the same, the phones will ring round-robin, not interrupting the sequence between one call and another.

Thus said, the way shared DN works on CME, is that once a phone takes a call on such a DN, that phone actually "becomes" that DN for the duration of the call.

To prove that, call a dual-line shared DN. While still in call, place a second call to the same DN. You will see that the second call is presented only the DN/ephone already on conversation. Hang up the first call, and all the shared DN will ring again.

As far as I know there is no way to change this behavior.

If you want to be able to have other phones pick up calls placed on hold, I suggest you use park slots instead.

PS remember to rate useful posts.