Negative, the stories I heard were about violating active military training areas, such as EBD37.
As for the transit tax, I think you may have heard about the microlight-specific overflying tax of 87 euro's for a 30-day period; this however is meant as a "punishment" for those Belgians preferring to fly on a French (or other foreign) registration. One can find indications that this tax will not be required from genuine passers-by; one example at
Aero- und Modellflugclub "Feuervogel" Bllingen/Belgium
((yes yes, this is Belgian, did you know there's a little corner of Belgium where German is the language? A lovely field it is, too)