Same thing with my GH3. It was annoying at first, but I got used to it pretty quick.

I edit most of my clips in the Trimmer, so this isn't an issue at all.

But if I bypass the Trimmer and drag an entire clip into the Timeline, I'll position the Play Cursor at the end of the audio (easy because the cursor will snap to it), press Alt + ], and BAM, the extra audio is gone.

Again, not perfect, but after a very short time I didn't even notice it. Maybe it's a matter of perspective because I've been at this since 1994 when computer-based editing was very, very iffy at best. My last project was the Edit From Hell - 518 edits in a 16 minute video. Most of these were audio edits that required me to ungroup the audio from the video (for almost every clip on the timeline!!) so that I could slice and dice the audio to match what was happening on the video. During the entire edit session, which took several days, Vegas never crashed - and I'm using my graphics card to accelerate timeline preview. At the end of the edit I touched up the audio using Vegas' exceptional audio processing capabilities. I have Premiere CC on my edit machine and, although it could be done, I wouldn't even attempt this type of technical editing on Premiere.

I'm not trying to convince you that this obvious bug shouldn't be sorted out, just suggesting a relatively painless work-around so that you can enjoy all the stuff that Vegas does really, really well.