WordPress.org

Can I use formatting HTML tags within tags?

No, all formatting text will be lost. You can use formatting outside, in which case your flipped text will appear with formatting applied to it.

Why some symbols are not displayed correctly?

Well, that's a question to browser developers, I think. Unicode character support is bit flakey in some of them, and not all characters are rendered properly. It also seems to be position and neighbouring characters related too. So far I've noticed issues with letter 'p', so just try to rephrase your sentences and experiment to get the best result.