We did extensive research on the subject, there is no mystery. iOS will <i>only</i> read MIFARE tags with NDEF formatted data.
If you write NDEF data to a formatted MIFARE card, it will be 'compatible' with iOS.<p>Otherwise, only the UID can be detected.
The real mystery is why Apple refuses to open the low-level read commands. (To read NDEF, or determine that the data is _not_ NDEF, you need to read the card.)