I came across a production HTML page which has no close tag for one of the input fields.
This production system has been running for quite a while and targeting only IE6 browsers.
I would like to do a check with everyone here, as i am striving to give a good reason to raise a defect fix, are there any good supporting reasons for doing such?

What is the doctype of the page? That should validate with an HTML 4.01 doctype. However, it will NOT validate as XHTML.