I have a customer that has an MICS with 5.0 SW with PRI and about 75-80 users. Customer is saying that as calls come in and are parked, as calls are picked up, the remaining parked calls shift for example from 102 to 101. I called customer and we tested it and it seems this scenario is happening. Any ideas? Below is their email to me.

Sometimes line 101 & 102 will ring in at the same time. She will answer 101 and no one is there. She will then answer 102 and it is the same phone number on ID from 101, that line (102 ) is the one the incoming call is on.

When more than one line is on hold, as someone else picks up 101, or the person hangs up on 101, each line still on hold moves up. So if 101, 102 & 103 are all on hold and someone else picks up 101 or they hang up, 102 will become 101 and 103 will become 102. This causes a lot of confusion on both her end and others trying to pick up the line that was on hold for them.

A little confused with some of your statements.
First - Someone is parking calls with F74 - correct?

How is 101 and 102 ringing at the same time and you also say "102 is the one the incoming call is on".

Is it an incoming call OR is it a parked call.
Then you say it was 101 and now it is 102. Wouldn't that be a shift up instead of down?

Also you say it is 5.0 software.
Someone else can agree with me or say I am wrong.
But my gut says that 5.0 is a bad software to be on especially with PRI. I could be wrong.
But if that was my site, I would try to get them to 6.1 or 7.1.

Give a little more info about the call path.
Call in, what ext answers and then puts it on Park. And then how does that call become another incoming call?
Are you leaving out that the Park has timed out and rings back to the one who put it on Park.
How quick do the parties answer calls on park?
Maybe extend the park timeout.

Just an expamle.
Call in. Recept answers and puts call on park. It parks on 102 because 101 is already parked.
101 gets answered.
102 caller gets tired of waiting, hangs up and calls right back. Recpt puts call on park-101 because previous 101 had been answered.
Person trying to answer thinks call is on 102, but it is now on 101. It did not shift.
Just a thought.
More info.

I agree 5.0 not a good one.....too many bugs.

Speaking of which I think that's exactly what you have, a rare bug.

Have tried rebooting the system yet?