Style sheet not reloaded on some pages when switching tree paths

[ddawson]

In some cases, when a page is switched to through the tree, its style sheet seems to disappear just after the page comes back into view. Examples of sites where this occurs, provided by user Cyan (not the same one on GitHub):

• http://anidb.info
• http://www.pogdesign.co.uk/cat/

Just as an initial guess, it looks like the problematic pages have external style sheets all with titles assigned in the link elements. I will need to experiment to confirm that, but it might be a clue.