A build step needs to monitor a repository for changes at root level only (depth=files).
Contrary to what is expected, the svn plugin does not distinguish modifications to files deeper in the tree from local changes at depth=files, and a build is triggered for every change in the entire repository (almost every poll, as this is a large project with many teams)

The expected behaviour could be achieved by parsing the output of "svn status --show-updates --depth=files", excluding the entry for "."

(I realize that polling might be running from the master, where no workspace is available and it could be not easy to implement this kind of action...)