Andrzej,
This is an unfortunate side effect of Mode C detection.
Mode S targets are 'relatively' easy to positively identify as they include the ICAO hex address. Unfortunately Mode C doesn't have the Hex address and is therefore much harder to positively identify. Lee has therefore had to develop a complex filter to try to identify and disregard our own transponder. The unfortunate side effect of this is that occasionally during rapid climb or descent, our own transponder fools the system and appears as a 'threat'. This was always going to be an issue when we decided to address the Mode 'C' transponder issue. Lee is still working on improving the filter algorithms. In the meantime please ensure that you are running the most recent software update and we just have to learn to understand and accept this anomaly meanime.
Regards
Peter
