When a custom connection is used on a location where three or more plate sections come together (e.g. a T-shaped plate construction, see below), the results in PLAXIS 3D 2012.00 are not correct.
In order for the custom connection to work correctly, the local system of axes need to be connected correctly. For the plates with the custom connection, and the reference part, this is done correctly. But for the third plate section that is connected here, the local system of axes is not connected properly. This results in incorrect transfer of displacements, rotations and forces between the plates.
Note, the number of plate sections mentioned here refer to the number of plate sections you will find after intersection.
This is solved since PLAXIS 3D2012.02
However, for the mentioned T-shaped plate structure, a workaround can be used if the soil-structure interaction between the soil and the rigidly connected plates can be modelled without an interface (and so tying the plate to the soil). One can remove the interface on the opposite side of the custom connected plate. This will give one single node for the two rigidly connected plates, and so all local axes are now coupled correctly.