Some customers use "hotfix distributions" rather than common release distributions with hotfixes applied.
Looking at their content, these "hotfix distributions" are equivalent to the release distribution with hotfixes applied. But they don't have any hotfix package actually installed. So installing a hotfix on them is not possible since it would ask to install all the previous hotfixes.
Hotfix distribution must include a base meta-package "providing" their correspondent hotfix package : for instance, nuxeo-cap-5.6.0-HF27-tomcat must include a meta-package providing the hotfix 5.6.0-HF27 to allow installing the hotfix 5.6.0-HF28 on it.