Radar gremlin

This is an old one, sometimes fighter air radars are losing exact fix on targets they were already tracking and for all I see they should still be able to do so.
I've seen this happen for an F-14 tracking a Mirage F1 at some 50nm
and now I got a save file for an F-15 on Su-17 at 12nm.

• load nofix.hpc
• group WLA (3xSu-17) is in front of CJA (2xF-15) at 13nm even for a blind to see
• run the game for 4 seconds for the next radar update ... nope, still uncertain contact only
• Why??

Debug just confirms the fact:
106541 search.c:884 - Radar Emitter=F-15 Eagle (Is) Target=Su-17 Fitter D, TargetRange=12, Radar LOS = (BaseLOS x weather_mod + 128)/256
106541 search.c:885 - Radar LOS of 135nm = (135nm x 256 + 128)/256 --> Radar LOS=18353/256
106541 search.c:891 - A RCS=152 TName=Su-17 Fitter D AName=F-15 Eagle (Is) Range=12 Die=44 aPD=70
106541 search.c:964 - B RCS=152 ARng=73 Arng=110 SRng=0 Srng=0
106541 search.c:968 - Target was previously tracked.
106541 search.c:1041 - Not Detected Su-17 Fitter D