Element fails to show in list of valid elements

I have updated my DTDs and generated new XSDs based on a transform provided to one of our support partners. XSDs work properly in Create in terms of validating all tags. However, I added back in the sl tag, which had been constrained. While a sample containing an sl tag validates, the sl tag does not appear on a list of valid elements. I also added the ol tag back in at the same time. It does show up in the list of valid elements.

Has anyone encountered and resolved this problem before?

Thanks