Analogue set (OLD Alcatel from '92-'93!) not releasing conv

[krzysioD]

Problem looks like this:

the A calls B, B hangs the phone (old Alcatel set from around 1992, was white, now it looks like greyish).
The "A" is still has a earphone in hands and hears like the conversation is not over (no proper tone).
The B is in state "BUSY", when calling from UA set or Analogue set.

Also if i pick up the earphone from analog set, i hear the "A".

This strange stage of "B" set takes a 3-5 seconds, then the conversation is finally disconnected.

Any hints?

BTW: replacing a 500+ old alcatel sets is not an option, previously there was a system like 1.4 with Z24 in step1, now eZ32 with brand new OXE.
and to have a full picture "normal" cheap analog sets work good. Client wants to have the old Alcatel phones working...