This post may be of interest if pass rendering with architectural material produces rendering artifacts in passes (wrong shadows or noise).
Few days ago Autodesk released Maya 2013 Service Pack 1. This release contains a partial fix which reduces some of such artifacts. We have prepared the second ingredient with completes the fix.
The archive ftp://ftp.mental.com/pub/ray-architectural-188.8.131.52.tgz or ftp://ftp.mental.com/pub/ray-architectural-184.108.40.206.zip contains updated architectural.dll (.so/.dylib) shader library for mental ray 3.10 on all platforms. It can be used to replace the library distributed with Maya 2013 SP1.
[Note: some versions of tar will present an error about a 0 block when unpacking the tgz. The last dll should still work. Check your permissions on Win64 machines if it doesn't. We provided a zip as well in case you are still concerned about the error.]
Together, MayaShaders.dll from Maya 2013 SP1 and architectural.dll from the ftp archive resolve all pass shadow artifacts.
Note that one has to use MayaShaders.dll from SP1, updating just architectural.dll will have no effect.
Hope this will help,