The tag is present in Lintian version 2.104.232. That is the most recent version we know about.
Lintian found a substvars file in the Debian diff for this source
package. The debian/substvars (or debian/
is usually generated and modified dynamically by debian/rules targets, in
which case it must be removed by the clean target.
Refer to Debian Policy Manual section 4.10 for details.