I can find no reference to P. joannisi feeding on Field Maple, so I can only suggest you take them home and try to rear them - it could be a very interesting record!
Actually there are images of (allegedly) Phyllo. acerifoleilla similar to yours here: http://www.bladmineerders.nl/minersf/lepidopteramin/phyllonorycter/acerifoliella/acerifoliella.htmso you'd definitely need to rear them out to convince anyone (including me) that they are not that species. Go on Paul - prove them wrong!
Will collect some next time i'm down there Dave.