As previously stated in this thread, Knockout is indeed supposed to go away after getting a melee kill, at least as of the most recent sandbox patchnotes (from early December, if I'm not mistaken). I haven't noticed this new Frontal Assault bug, even as someone who mains that subclass (granted, I haven't been playing much Destiny recently). I'll be on the lookout for it next time I choose to hunker down in PvP for a bit. The only new bug I've noticed is this apparent state where your primary is unloaded for some reason, though I thought it was just because I'd swapped weapons too late before a match started. But I think it's safe to say I've both seen and heard enough people make comments about it to realize that my case wasn't just an isolated incident.