Audio is slightly boosted when exported through Render Queue to H264

Discovered a potential bug today that will slightly boost audio (by less than 1 dB) when exporting through AE's Render Queue 'H264 - Match Render Settings - 5Mbps' Output Module preset. This resulted in clipped audio (hitting reds) in my final output. Audio was an unchanged WAV music track that was quite heavily limited (metal genre). 

I was able to solve the issue by exporting the comp to ProRes 422, importing to a new Premiere timeline and exporting to H264. This gave me an H264 at 5mbps that did not clip.

I expect this is likely due to mp3 compression, and may be known to low H264 bitrates, however thought it odd that the problem did not occur when exporting with the *same* settings and bitrate from Premiere.

Note: I did not try to repeat the bug via Media Encoder (don't ask me why - was on a tight deadline and went on autopilot as there were a couple different variations of the export - Prem was quicker in this instance).