The difference you observe for reduced force in diagrams for buildings can be observed for seismic load cases in RSA 2012. It is resulting from different sequence of calculating linear and quadratic combinations.
In case of base shear and the table of reactions first for each vibration mode reactions for all nodes are linearly combined (added) and then for these sums CQC quadratic combinations between vibration modes are calculated.
In case of reduced forces in RSA 2012 first for each node CQC quadratic combinations of pseudostatic forces between vibration modes are calculated and then these quadratic combinations are linearly combined (added) for all nodes. It results in difference in final values.
It is planned to unify these methods - reduced forces will be calculated using the same sequence as used for base shear and the table of reactions. I will notify this post as soon as such change is available.
This issue has been addressed in SP3 to RSA 2012 which can be downloaded and installed using Live Update or the following link:
Mind to select the correct version of the SP (Professional or Standard version as well as 32 or 64-bit OS)
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