I wish I could help with this but alas, I cannot. I haven't used Vegas in a very long time and when I did I
actually would encode using WMV. After switching to Adobe After Effects/Premiere, H.264 just seems to be
built-in with it.

I have used the K-Lite codec many, many times and have not found anything 'misfunctioning' as you mention
although, I'm sure I haven't utilized every codec in the pack itself.