Ghost tags (TI TRF7960)

Hi

I'm using the TRF7960 reader from Texas Instruments to read ISO 15693 tags.

When making an Inventory call to two tags at the same time, the tags sometimes replies with the wrong UID's. (It's just like a ghost tag has replied instead of any of the two tags).
When I get a wrong UID at the Inventory call, the tags don't answer when i make an addressed Read Multiple Block call (not surprising).

The ghost tag phenomena mostly occur when the tags are in a position where they are hard to read (bad angle, or long distance).

The tags are of the same type. They have anti-collision support. I have tried with different tags from Melexis and ST Microelectronics, with the same result.

I have tried using different settings; AGC on/off, AM/PM, High/low data rate etc.

Is there anyone out there that has experienced the same phenomena? Or can anyone make a classified guess what is wrong? Shall not the reader make a CRC check to see that the replying UID's are valid?

Best regards,
Jörgen