I'm pretty sure you have a different problem.I just got the same problem described in this thread.
It's not a bug, but you are free to use any software of your choice!I'm probably not going to use Audacity again after that, but the software has a bug in it that is not allowing users to record the full range of sound in some situation.
This is normal when you recording with one microphone in mono with a stereo interface.* If you connect another microphone you should be able to get to 0dB (100%) with both inputs combined into one mono track.
If it was not reducing the signal, you could potentially get clipping with both channels combined to mono but the clipping indicators on the interface don't show the combined signal so you'd have to watch the software-meters to watch for clipping.
It's really not a big deal. You're not loosing quality (especially if you're recording at 24-bits**) and you'll probably be adjusting the volume after recording anyway. And, the clipping indicators on your interface should still be working... The red clipping light should come-on when you hit -6dB (50%) in Audacity (assuming you're using only one input/microphone).
If you record in stereo you should be able to get full volume but you'll get one silent channel and then you'll have to convert to mono.
* You have a 4-channel interface, but I recently read on the forum that it records two stereo pairs. But, Audacity will only record two channels.
** Your software is set to 32-bits but the analog-to-digital converter in your interface is 24-bits, so that's a software conversion. Audacity (like most audio editors/DAWs) uses 32-bit floating-point internally and there are good reasons for this. (REAPER works at 64-bit floating-point.)