I don't know the settings or the exposure time you used... but I believe you had the pleasure to experience the 'hot pixel' effect: with long exposures (anything over 4 secs I think), your image will have these strange multi-coloured pixels (also called 'static noise') all over, especially in the dark areas (at least that's where they are most visible).
That's normal for digital cameras; there's nothing wrong so far with your cam or filter.
I think most cameras can compensate for this by adding 'static noise reduction' by means of a second, equally long exposure, completely black this time, and by somehow calculating the difference between the two, thus eliminating these hot pixels. For example, if you have eight seconds of exposure time, your camera will be 'locked up' for an additional eight seconds to allow for the pixel reduction process. I don't know how your cam deals with this... I just know my camera does provide this kind of noise reduction... check your manual to see if and how your camera can do this...
Anyone who ever took night shots with long exposure times must have experienced this... and can probably give a more exact response ;o)

We do not see things as they are. ǝɹɐ ǝʍ sɐ sƃuıɥʇ ǝǝs ǝʍ