The issue at hand is the following:

Project contains and svn url of the form: $SVN_ROOT_PATH/trunk
Each node sets $SVN_ROOT_PATH to the SVN mirror closer to the node location.

This allows us to have fast checkouts etc.

Problem now is that Jenkins seems to think that the master evaluated SVN URL is different than the workspace checkout path of a slave and triggers a new build.
This happens until it happens that the slave that picks the build is using the same mirror as the master.

Setting polling to master only (via the magic property) does not fix the issue since the problem is not polling but Jenkins trying to be smart and detecting that the workspace has a different SVN URL than the configuration.

Not sure how to tackle this but I am having a look.