After Minecraft finishes loading and gets to the menu screen, the game output window goes totally unresponsive and frozen without even getting a "(not responding)" in the title bar thing if it was the focused window, or goes blank white if it wasn't.

Curse forces the old launcher (their changelog mentions a compatibility change-appears the new launcher can't handle modpacks), so I'll be using that, most likely. I may never go back to actually using your launcher.