Directed BLF Call Pickup Issue (Shows nummer of Extension)

Hi there,
we use Aastra / Mitel 6869i

If a customer is calling my colleague i see this on a BLF key.

I only have to push the BLF button of his externsion and i pickup the call.

The Problem:
I see the number of my colleague on my phone, but i want to see the number of the customer,

Buttons configured as BLF/xfer

Can anyone help me please?
Or is this maybe an issue with FreePBX?

Info Update:
We use P-Asserted-Idendity on every extension