Check this thread out http://www.mazdas247.com/forum/showthread.php?123827975-Upgrade-on-2006-rear-suspension-to-2012
Davicho put 2012 springs on his Mazda 5 and seems to like them.
Yes kw you beat me to it. Although I sold my 2006 and now have a 2012. I was going to say that Franzy just answered his own question. Since the issue was fixed on 2012+ models as Franzy stated then just upgrade your rear springs and shocks to a 2012+ model. They bolt right up and all other components such as as the control arms and what not are identical parts. It may also help if you upgrade your rear sway bar to one from a 1st generation Mazdaspeed3.