D800 builtin flash fails

I keep a small (No, not the Nikon device!) GPS in my D700 hot-shoe. If I pop the flash up, it looks OK, but clearly it fouls the GPS, and doesn't come right up, and won't fire. It seems that unless the BIF is fully up into position it doesn't make some hidden contact.

Is it possible that there is some small bit of fluff or dust which fouls the D800 BIF, and prevents it rising all the way into position?

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Richard