mesh missing?

Hi I am trying to remodel my character and have got to a point im trying to weight paint the model.

Now up to now the model moves as expected except the glasses on the head. I have tried to seperate the glasses mesh from the head but when i go into edit mode the mesh for the glasses disappears so i cant move it to another layer. if i leave it where it is the glasses move incorrectly.

Why is the mesh for the glasses disappearing. Anybody got any ideas? ive put a few shots so you can see what I mean.

Thanks for the help.

I have uploaded the blend file too just in case you can see what i have missed.

Alt+H to unhide in edit mode