[formerly_proven]

The width of the area around microwave doors looks suspiciously close to lambda/4 for 2.4 GHz (~3 cm) on pretty much every microwave I've ever seen - I'd almost be surprised if that construction isn't tuned to reflect 2.4 GHz, which would make it a very leaky container at say 0.9/1.8 GHz.

[willis936]

I think you should double-check the harmonics that would get passed relative to a quarter-wave mesh.

[Johnythree]

Yes, microwave ovens use a tuned slot to seal the door. It's basically a half-wave stub.