All reports of menu-icon-not-in-xpm-format for the archive. The extended description of this tag is:
Icons in the Debian menu system should be in XPM format.
While other image types (e.g. png images) appears to "just work", window managers are not "required to support them". Accordingly using non-XPM icons could break interoperability.
Refer to Debian Menu System section 3.7 (The icon field) and https://bugs.debian.org/591812 for details.
This tag has not been emitted in any package tested by Lintian.