MIG,
So would I! My guess is that the majority of current installations are STCs and thus often held to a lower standard than a system installed as OEM. This has been a bone of contention with the authorities - especially when they just don't have the expertise available at the local level.
Not strictly aircraft EMC, but I once got involved with an ILS interefence issue at a European airport. When the Flight Inspection checks were carried out after hours, there were no effects recorded but aircraft had glideslope issues (backed up by data analysis) during peak periods. My suspicion was that a mobile phone tower was causing the problem, which disappeared as phone traffic wound down.