When looking into the "customize airport position" menu, it shows points to the file ZMIA_ADEX_RGM.BGL. The parking positions however are in the file "KMUA_ADEX_RGM.BGL".
This worked fine in GSX until a few days ago. Since then, I reinstalled GSX and I installed KMEM...
It's not possible this could have anything to do with the latest update. The only possible explanation is that you didn't had that other file before.
This problem is caused by the scenery having two valid AFCADs, but with parking positions in one of them. GSX cannot possibly know which one is correct, so it picks up the first one it finds.
Whether this can be fixed or not, depends how the AFCAD is made. Are those other AFCAD all using the same ICAO code or, like many developers, use different (fake) ICAO codes, to represent additional features like seaplane bases, helipads, etc. ?
If they used a fictional ICAO, GSX has a way to sort these issues, using the Airport_Visibility_XXXX parameter, discussed in the manual, and here too:
http://www.fsdreamteam.com/forum/index.php/topic,12516.msg94925.html#msg94925It was always like this, which is why the solution was already present in the previous GSX version, and explained in the manual.
If, instead, the developers have two AFCADs for the same ICAO, both containing parkings, that will be a bit of a problem, since GSX will consider to be both usable, but will use only one of them.