Reserved word 'script' embedded in id tag - id can't be referenced

Question

This is a new one on me.

In FF 3.6.3, use of the word 'script' in a tag id seems to make the id return null when searched on with document.getElementById.

Thus document.getElementById("blah_script") returns null from <div id="blah_script"></div>.

Understood that 'script' in general is a reserved word, but I didn't know it was so spooky that a mass-adopted browser would care if it was in a tag id with a preceding expression for disambiguation.