When using streams in the Perforce plugin the following command is issued.

[jenkins_test] $ "C:\Program Files\Perforce\p4.exe" workspace -o -S //Streamed_Depot/MyStream NikSanWS

But this doesn't perform a switch workspace view, so perforce is still working the stream selected in P4V etc rather than the one specified bu the plugin. A fix is to supply an extra -s parameter like so. (only when dealing with streams)

[jenkins_test] $ "C:\Program Files\Perforce\p4.exe" workspace -o -s -S //Streamed_Depot/MyStream NikSanWS