Sometimes when defining a distributed load system or a prescribed displacement, the point numbers in the 2D model visualization do not match the point numbers given in the dialogue to set your load values:
The point reference in the Distributed load dialogue could be mixed up, depending on the draw direction of the line. The graphical representation of the distributed load and the prescribed displacement in the 2D model visualization is the correct distribution and that will be used in the Finite Element calculation.
This issue for the dsitributed loads is fixed in 2D2011.02. The issue for the prescribed displacements is fixed in PLAXIS 2D 2012.00