I'm trying to hack ACF plugin until I get a response but I don't even know where to start looking.
It seems wordpress is stripping the semicolons to prevent the serialization to break… or something else, but I bet ACF plugin is relying on it.
Specifically they are fontawesome characters (high numbers) that I want to be displayed inside a select box (the font doesn't render in a drop-down select) and despite the semicolons are not rendered, the browser fixes most of them (the lower numbers) but the last third of icons render as a square.
I tracked the issue to the semicolon stripped from e.g.
&#x f116; at some point, becoming
 (stripped semicolon)
I've read before something like "allowed characters", but I can't find it anymore :(