You might have better luck if you send a bug report or email to the mailing lists, they can't fix a bug if they don't know it even exists.
I swear it's possible you're overlooking an option or configuration setting, but I don't know for sure.
It is however unwise to be using 4.3, it is no longer support.. and a couple erratas have been released since then.
Can you at least post your 4.5 dmesg, the xorg.conf file.. your Xorg.0.log file.. and.. perhaps all of the above using a 4.6-beta snapshot?
Good luck..