I am Almost 100% positive it's only a measurement of what your hdd space will be in recording time, that'll probably be in .wav file uncompressed so when you save a song (you'd notice even short ones are pretty big) as mp3 you won't notice like much change in the size.
As for it always staying the same... Maybe the program isnt refreshing the information?

have you got the Beta latest release? I think its 1.3 Beta, While not much different I also found the plug-ins page, some of which are quite interesting, all in all I have found this program Incredibly useful as it's free, and with a little know-how ANYONE can record good quality music with it.

Anyone know how to use Lisp? Nyquist????

Personally I only use Audacity for multi track recording, then move onto programs like Flstudio XXL to put the song together, (im on my own no band behind me so its easier to go one part at a time I've found) and use a very useful plug-in called Izotope Ozone - While expensive I have found that I can even bring long dead music back to life with a really beautiful effect, not making the music muddy in parts and lifting others but allowing you to really clean up and lift the parts you want, and cut the others.

Or use it individually on each instrument to develop "that tone", you know the one, the one all the pro's seem to have, the one that no matter how hard you try, your amp/guitar etc combo never quite seems to acheive perfectly.....