Is there a fundamental difference in function of the audio gain level of an event versus the volume set with a volume envelope?

I ask because of what just happened. I had an audio event with a really low level. I normalized it, which brought it up about 30dB. I then used a volume envelope to control it, as I normally would for audio events. And I had the track compressor going with a 6:1 starting at -12dB, autogain turned off, all the rest default settings for that preset.

I soloed that track and noticed that the compressor was compressing heavily, and my main output was showing the level for that track at down around -18dB. But the input gain window in the compressor was showing it hitting -6dB. This didn't make sense to me.

So, I then tried bringing my volume envelope to 0dB for that event, and dropping the gain on that event by -6dB. By doing this, the compressor was only triggering occassionally as it should, and my master output level while soloing this track was at around -12dB, and the compressor in and out were around -12dB.

It's almost like the compressor didn't see the volume envelope I had set up earlier, which on the lounder parts I had it down as low as -18dB.

Any idea what was going on?

Thanks.