Hello,
This is a known limitation of the framework search algorithm, see here:
http://www.telerik.com/automated-testing-tools/support/documentation/user-guide/code-samples/html/search-control-type-by-partial-attributes-fails.aspx
In this case Find.ByContent(partial text) finds the first element matching the given criteria which is html:0. Trying to match the given element type fails so the end result is null. If you search by AllByContent you will get a number of elements instead, for example html, then title, then body, etc. See the attached project for reference.
I hope this helps!