All reports of extended-description-is-probably-too-short for the archive. The extended description of this tag is:
The extended description (the lines after the first line of the "Description:" field) is only one or two lines long. The extended description should provide a user with enough information to decide whether they want to install this package, what it contains, and how it compares to similar packages. One or two lines is normally not enough to do this.
Refer to Debian Developer's Reference section 6.2.1 (General guidelines for package descriptions) and Debian Developer's Reference section 6.2.3 (The long description) for details.
This tag has not been emitted in any package tested by Lintian.