Well I'm an idiot - the fulltext index on page_text was missing from a default installation. It didn't break searches but probably slowed them down tremendously. Also set engine to MyISAM on page_text to avoid cryptic error messages from MySQL.

// UK lang variables

tinyMCE.addToLang('layer',{
insertlayer_desc : 'Insert new layer',
forward_desc : 'Move forward',
backward_desc : 'Move backward',
absolute_desc : 'Toggle absolute positioning',
content : 'New layer...'
});