This has been discussed so many times on the forum: default FSX jetways ARE bugged. There's just no way to make them work with all planes, without side effects like wheels sinking. This bug has been acknowledged by Microsoft since 2007 when the SP2 was released, but it hasn't been fixed so far.
All our sceneries only change the visual model, but the actual animation is controlled by FSX.
We'll hope to fix this in the future, by switching to SODE jetways (SODE is a free program that replaces the FSX jetway system), because we are currently working on integrating it with GSX right now, and we expect all our future sceneries to be made with this new system, which will work better.
It's also possible we might do updates to existing sceneries to use the SODE system as well.