My neons have the same problem as the original poster. (These are not just bumps or blisters that result from getting rubbed or knocked that pop and go away)--

Mine occured in a 29 gallon tank that had been set up for well over a year and had no previous problems. The neons had lived in the tank for this entire time with absolutely no symptoms. My son wanted to add a pair of sword tails to the tank and the female died within days--(We added her to the tank, she gave birth to 2 babies, and died a few days later) I do not know if this had anything to do with the problem. We also had added some live plants, which also could've carried something into the tank-- These both occurred shortly before the problems arose. (I'm assuming that something was brought in...)

At the end of July 2011 (note-- it is now mid-November), I noticed one of the 11 neons seemed to have a whitish appearance to it's upper lip. This slowly (probably over a few weeks) developed into a "bubble"-- I read on-line that it was probably a blister, would pop, and all would be fine.

A second fish began to develop a "bubble".

The bubble on the original fish grew to the point I was sure the fish couldn't be getting food, it began to rub in on things, it popped-- and I thought the problem was over for that fish and that the second fish would follow suit.

But, then what appeared to be the same fish developed a second bubble-- Now, the bubbles were not as "bubble-like", but looked whitish and were no longer smooth--

I treated the tank with Fungus Guard, repeating the treatment when it was ineffective the first time. (This did not help)

After reading more, I thought perhaps this was columnaris-- I kept treating, watching, changing water, waiting, watching, trying something new--

More neons continued to develop mouth growths, one began to get a whitish cast to it's body, another that otherwise appeared fine began to fade in color--

I finally read about Neon Tetra Disease and decided to remove ALL the neons from the tank to a 20 gal. tank (that had been fully cycled-- we had a lone, huge, ancient groumi in this tank that had recently died and I had left the tank set up after his death)-- I WISH I would've done this transfer earlier, but I think i was hopeful that this was just a "mouth injury" and would disappear--

It's now been almost four months--

I STILL have 11 fish. The original 2 look absolutely horrible (At least, I assume these are the original 2). All of them ACT perfectly normal-- they still swim around, they still eat (or try to eat when they have large growths). I often thought of taking the "better looking" fish out and seperating them, however all fish seem to have been affected in some way-- I have 2 that have a cloudiness to their bodies (like excess slime coat) in addition to the their mouth-issues, I have 2 that have very noticeable deformed (by bubbles that have grown and popped) mouths, I have one that has a black spot under one eye (in addition to some minor mouth bubbles)-- The common factor is the mouth bubble.

I am religious about water changes and water quality-- I have kept fish for over 20 years and have NEVER had problems like this, and have had fish that have lived for years and years and years! (I rarely have established fish die!)

The neons have been treated with Jungle Fungus Guard, Marycyn, Marycyn 2, Copper Safe, Melafix (yes-- I was using a scatter-gun approach, feeling that at this point, there was not much to lose)-- NOTHING has improved the fishes' symptoms in the least.

I have no clue what this is-- I have researched and researched and researched and have read of other people having similar problems, but no one seems to post what the final outcome is (I am assuming the fish will eventually die) or knows what the problem is or how to successfully treat it.

I have been calling it "neon tetra disease", but am not really convinced that is what it is. (They don't seem to match the appearance I've seen in photos.)

Anyway-- I am posting this in case anyone has had luck in treating something like this, and to provide some information for someone having a smilar issue in their tank-- my advice is-- if you have a neon that develops a "mouth bubble"-- ISOLATE IMMEDIATELY.

(sorry if there are type-o's/miss-spellings. It is late and my brain is not functioning properly!)