Strikethroughs disappearing on 2.9.2 can insert only with HTML tab

Just upgraded to 2.9.2
Published a post with spelling/grammar errors and corrected it. I inserted an UPDATE COMMENT and left the errors in place with strikeouts. While editing the strikeouts showed up but when I hit the UPDATE button and looked at the finished product the strikeouts were gone. Tried it three times with the same results so had to present the thing without the strikeouts, which wasn’t as funny.

I found out that if you’re using the VISUAL tab and use the strikeout button it shows up fine on the screen but if you hit SAVE DRAFT the strikeouts disappear.

Same thing happens if you use the strikeout button while using the VISUAL tab and switch to the HTML tab: the strikeouts disappear.

If, however, you do the strikeouts (del’s) while using the HTML screen the strikeouts stay all the way through to finished, published post.

I was using the theme Blue Grace 3.1 by Vladimir Prelovac.

I also tried the strikeout test with several other themes:
WordPress Classic 1.5 by Dave Shea
Organic Theme 1.9.2 by The Forge Web Creations
R755 4.2.0 by varometro
Alkivia Chameleon 2.3 by Jordi Canals

That seemed a sufficient test. The same thing happened with all of them.