I've only just found out about this, so apologies if it's old news, but Jeppesen and Garmin issued a nav data alert dated March 20th covering errors in the database used in Garmin GPS units.
A problem has been discovered in NavData Controlled Airspace, Restrictive Airspace, and FIR/UIR boundaries, which can cause a misrepresentation of the boundaries for some airspace. Do not use any of the boundaries for reference or navigation. Until further notice, please refer to information from other publications such as paper charts as your primary source for boundary information. (From the Garmin web site - FS)
The direct link to the Garmin notice is
here and the Jeppesen list of the areas affected is
here.
It looks as if the only error in the UK is at Stansted, but there are many others in Europe.
Perhaps the update that they are presumably working on will fix the ATZ diameter and MATZ stub problems too.