The problem is that your flash is reflecting off the moisture drops straight back into the lens. The moisture drops are in the air and come from breathing, streams, waterfalls, etc. They are not on the lens (normally) as they wouldn't reflect the flash if this was the case. The way to beat this is to get your flash away from the camera ( maybe a metre or more, this means the path of the reflected light is not straight back to the camera).
The camera probably flashes more than once and this can be a problem triggering slaves, although there are some products out there that deal with the problem of multiple flashes, thay have mixed results. :-\
You might try turning the flash off, put the camera on a longish exposure (2 - 4 secs) and fire a flash gun manually whilst the shutter is open. Either with the camera on a tripod if you there is any ambient light or you can do it hand held if you have total darkness. I have used this method with my SLR to great effect. Ambient light is only a real issue if it is straight in front of the camera, in a cave light levels are quite low so it dosent seem to matter even if you hand hold the camera. It's a bit try it and see, but with a digi camera its no real issue to retake the shot.
If you want to use the camera flash to trigger a slave then you need an infra red filter (piece of exposed film is ideal, see who said film was obsolete) over the camera flash and use a slave that triggers off infra red (Firefly).
Hope this helps.