Why Invalid HTML stored in a nvarchar(MAX) makes a select slow?

Why Invalid HTML stored in a nvarchar(MAX) makes a select slow?

I have a nvarchar(max), null column in a table storing HTML. If the HTML
is invalid, simple select takes 2-3 seconds.
Any ideas why?



UPDATE
select ResearchAdvice FROM Subsection where id = 97227
Broken HTML
<P>Possible new Us: <STRONG>Sung Won Park</STRONG> (Choi &amp; Kim),
<STRONG>HC Lee</STRONG> at Kim &amp; Chang. Names came up a little late in
the day, not enough to inclu