[JENKINS-18898] Comment.

Unclear what Run.getEnvironment is supposed to return after the build is complete.
In particular, SubversionSCM calls this during polling to substitute variables in e.g. repo URL.
Presumably in such a case node-specific variables such as ToolInstallation.home would be irrelevant.
But in general should this reflect the “current” computer (if any), or the computer on which the build ran?