I have the same, double height. There just is not room enought in a single dekker TB for it all.
If the option i mentioned is unticked, and crx's suggestion is not it, try ticking the option i seggested, applying the change, rebooting, and then unticking it. Windows can on ocasion, say 'i am doing A' and actually do 'B'. The tick/reboot/untick usually forces the check box to actually report the tru state of affairs, rather then get it wrong.