Has anyone ever found a resolution to this? I have another site that this popped up on.
7200s v4.75 all iDCS 28d Phones analog lines.

A call is transferred to an extension and when the user picks up the handset the call goes to speakerphone with no way to take it off without putting them on hold and picking it back up. They had the issue on the previous 7100 and i have swapped out phones but it still comes back every once and a while.

Just curious to know, is headset mode activated on the extension?

No.
This issue has been discussed here and it's documented on old known issues but i've never seen a resolution or an explanation as to what causes it..

Does it seem to follow a specific lot number? Awhile back I had a lot of Idcs 28 buttons with bad handsets transmitter wouldn't transmit. All was the same lot.

We have the same issue, ours is a moisture problem. Once it happens the phones need to be replaced, they never dry out.

I never pulled one apart. What kind of hook switch is it? Mechanical, Carbon, Optical or something else?