[azapa]

i am not the one to answer this question, rather I am the first on the scene. You should be able to hold your breath with your mouth open. It is your epiglottis (valvey thing at back of throat) that closes everything in. If you over fill your lungs (packing) you could have quite some strain there, but hard to imagine it entering your mouth.

could you describe your problem a little better? does this happen at depth or on dry land?