Avidemux changing audio bitrate

[Soundsgoood5]

I'm clipping out the relevant parts of my own gaming recordings to save highlights. I found out that the videos I export from Avidemux have audio that is Variable Bitrate, when the videos I put in have audio that is Constant Bitrate. I'm not a very experienced video editor, my understanding is that Avidemux would have to actively do this, though I didn't want it to re-encode anything. Looking through the settings, nothing is showing it's actively set to re-encode anything, and it's even instructed to just copy the audio format (AAC, etc.) from whatever it was before. If I put in a .mp4 and set Video Output to "Copy", Audio Output to "Copy", and Output Format to either "MP4 Muxer" or MP4v2 Muxer", the output changes.

I'm very interested in solving this. Although it's minor, I make a lot of clips, and it bugs me that this actually changes the audio. (I tested that two seperate instances of the same footage clipped in Avidemux has the same audio, but slightly different audio compared to the original via looking at their waveforms in Audacity.)

I hear other clippers like LosslessCut also use ffmpeg so I'd rather ask here than try a different tool that might have the same issue. Any ideas? Some help would be much appreciated.

[eumagga0x2a]

AAC is an inherently variable bitrate codec. Avidemux doesn't change anything when in copy mode. However, I could imagine that whatever application has created the source MP4 file, it might have added padding after the end of each audio frame to make all MP4 audio packets of equal (bigger) size. Avidemux would then discard any junk after the end of an AAC frame, revealing the variable bitrate nature of the stream without altering the actual compressed audio data.

In doubt, please provide a short source video as a sample via WeTransfer, Mega, Dropbox or Google Drive.