unexpected "remote mismatch diagnosis" generated in IRT operation mode

If IRT is used and the Profinet IO Device is the last in line although everything is fine in principle the device may report a diagnosis "remote mismatch, no peer detected" for its unconnected network port.

This issue occurs when Siemens TIA Portal V15 is used with e.g. CPU1500.

The IO Controller activates the "SyncMaster"-check on the unconnected port of the IO Device. This causes the diagnosis mentioned above.

With some interpretation the Profinet specification can be read in such a way that in this specific scenario this generic diagnosis message shall not be reported.

This issue was introduced in PNS V3.12.0.12. All older versions are not affected.

All versions of PNS v3.13.0.x are affected as well.