IE is responsible for 4/5 of the bugs. Color me shocked.
This isn't about assigning blame, it's about empowering developers to be able to use flexbox today.
IE12 will be Win10-only (at least it won't run in Win7 as the normal support ends very soon) If the rumours are true, IE12 will come without the IE compatibility modes (IE7-10). And IE11 will ship as legacy browser next to IE11 for corporate users. So fixing the bugs in IE11 is even more important.