Well, that upside down question mark is due a wrongly formatted MathML code.

Your formula is:
matrix {# {italic "G"_italic "x" = left [ matrix {{-italic "1"} # italic "0" # italic "1" ## {-italic "2"} # italic "0" # italic "2" ## {-italic "1"} # italic "0" # italic "1"} right ]} # {"(1)"}}

If I just delete the first #, the question mark is gone:
matrix {{italic "G"_italic "x" = left [ matrix {{-italic "1"} # italic "0" # italic "1" ## {-italic "2"} # italic "0" # italic "2" ## {-italic "1"} # italic "0" # italic "1"} right ]} # {"(1)"}}

I'm not a MathML syntax expert, but I guess the formula was just incorrectly formatted?

Kind regards,
Joren

I can't see anything wrong with the MathML file. It looks like the first empty element before '#' sign is caused by miss parsing the mspace element in the MathML file. The formula editor can ignore the first mspace or add '`' for spacing in the converted equation.

(In reply to comment #2)
> I can't see anything wrong with the MathML file. It looks like the first
> empty element before '#' sign is caused by miss parsing the mspace element
> in the MathML file. The formula editor can ignore the first mspace or add
> '`' for spacing in the converted equation.

But, why you need the first # in the beginning of the formula? We could try to avoid this problem but, this seems to be a formula problem.

(I tried to open this file in Firefox, and it open it correctly)(In reply to comment #2)
> I can't see anything wrong with the MathML file. It looks like the first
> empty element before '#' sign is caused by miss parsing the mspace element
> in the MathML file. The formula editor can ignore the first mspace or add
> '`' for spacing in the converted equation.

It seems we need to improve our MathML import code... Maybe I can try to look at this in this week (I'm really busy, but, I can take a look....)