SAK-23266 introduced the fmath editor. The editor stores MathML data in the data-mathml attribute.
In 2.9.2-rc01, the FMath functionality will no longer work because of this Antisamy restriction.
1) Login as admin
2) Go to mercury site -> Announcements
3) Add new announcement
4) Choose Fmath icon in CKEditor (2nd row, far right)
5) Create new equation (just enter numbers like 12345)
7) Attempt to save