Yeah, my copy of Opera does the same thing - doing some reading, it seems to be a problem with Opera.

Instead of using Webdings, you could use Unicode. You don't need to specify a font name, just put the code where you want the symbol. So put #9650; for UP, #9660; for DOWN, #9654; for RIGHT and #9664; for LEFT. To make those work add an ampersand before the # and don't forget the semicolon at the end.

The four symbols below show up fine in Opera and Firefox, all close to the same size as they should be, but come up quite different sizes in IE7... which seems to be an IE7 thing.

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