As far as I know....
Amateur astronomers have been observing these flashes for a long time.
Until recently, lunar flashes were dismissed as imagination, camera artefacts, and other lame excuses.
With the digital age and internet, and amateur astronomers catching stuff on video, looks like the so-called "TLP" (Transient Lunar Phenomenon) are being recognized as a real (and common) event. Here's what Wikipedia says about TLPs: http://en.wikipedia.org/wiki/Transient_lunar_phenomenon
I was researching this a while back, and found that NASA has a program whereby amateur astronomers around the world can submit their images and videos. However NASA do not apparently share this gathered information publicly.The website to the NASA program is here: http://www.nasa.gov/centers/marshall/news/lunar/
I have seen some of the videos on youtube (there are only one or two vidoes on the above NASA link).
The standard theory goes something like this: the meteor impacts the moon, and due to kinetic energy, melts the lunar ground and thus gives off a glow. The problem with this is that anyone can see, that the flashes resemble more a camera flash than red hot lava, and the flashes appear disproportionate to the meteor's size. To my eyes, it looks like static electricity, just on a larger scale.
I could not find any details on the size of these meteors, however there are some pretty good observations and data on meteors and fireballs entering the Earth's atmosphere. they tend to "burst" or vaporize in mid-air, with only small fragments reaching the ground (and not leaving any craters).