Hi Mathias
Yes. This seems strange. The setting of the MASK bit must not influence the status bit being set. Are you able to see his behavior on a regular basis or is this intermittent? Also, the default value of address 0x7D must be 0xF7. Can you try reading that register value immediately after a software reset, without performing any other actions? Do you have multiple ICs? Do you read the same register value in those ICs as well? Can you share your communication port scope plots? Try to see if you can write to that register with the value 0xF7.
Regards
hmani