physik wrote:

This is a bug about the mathoid-server component.

When MathML input is used to convert MathML generated by LaTeXML via the mathoid-server to SVG. A problem occours while trying to send back the original MathML that was used in the request.
This probem occours if the original MathML request contains special characters like

Fun fact, bugzilla cuts off all input that comes after an Astral plane character. Instead, I'd recommend just writing out its U+XXXX number.

physik wrote:

Oh you cant use these characters at bugzilla. It's a bug in the bug tracking system.
See
https://github.com/gwicke/mathoid/issues/3

Change 119953 had a related patch set uploaded by Physikerwelt:
Fix: Remove MathML out if used as input

https://gerrit.wikimedia.org/r/119953

For reference, the character in question is:
U+1D49C MATHEMATICAL SCRIPT CAPITAL A

[Upstreamed the Bugzilla problem as https://bugzilla.mozilla.org/show_bug.cgi?id=986448 ]

Change 119953 merged by Physikerwelt:
Fix: Remove MathML out if used as input

https://gerrit.wikimedia.org/r/119953

Change 120182 had a related patch set uploaded by Physikerwelt:
Fix: Remove MathML out if used as input

https://gerrit.wikimedia.org/r/120182

Change 120182 merged by Physikerwelt:
Fix: Remove MathML out if used as input

https://gerrit.wikimedia.org/r/120182