When recently compiling a program requiring libglade, it complained that libxml2 was missing, because libglade-dev is not loading libxml2-dev - which seems to be required for builds using libglade.
I believe the problem is traceable to gtk2-dev not including shared-mime-info-dev, and shared-mime-info-dev not including libxml2-dev and glib2-dev. Doing this pulls up libxml2-dev as needed.
Since shared-mime-info is a dependency of gtk2, it makes sense to have shared-mime-info-dev as a dependency of gtk2-dev. And similarly, since glib2 and libxml2 are dependencies of shared-mime-info, it makes sense for their dev versions to be in shared-mime-info-dev.
Alternatively, libxml2-dev could be added as a dependency for libglade-dev.
Not sure why this has not previously been an issue.