As shown in this commit associated this this JIRA, https://github.com/hibernate/hibernate-orm/commit/9ad030aee66f9ece98df2c968c76778b21a39024
you'll notice that both XSDs have the right information. In fact, what you suggested is precisely what I did yesterday before making these changes as you'll notice I added constraint-mode to the 2.2 orm_2_2.xsd file.

Are you positive you're looking at the right files or the right branch? Be sure to look at master.