The Guardian Druid T15 2P Bonus should give you stacks of Improved Regeneration, up to 10 stacks, when you dodge an attack while Savage Defense is active.
In fact the stacks are applied by every attack on you. It doesn't matter if Savage Defense is active or if the attack is dodged at all. So you basically have 10 stacks after 10 hits on you.
Second point is, that Frenzied Regeneration isn't affected by Improved Regeneration in any way. Per stack the heal should be increased by 10% to a maximum of 100% at 10 stacks. The healing isn't increased and the stacks remain until they run out after 10 seconds of not being hit.
The screenshots i attached show me using Frenzied Regeneration with and without the stacks and you can clearly see, that the heal amount is the same.
For some reason the screenshots are't attached...
First Screenshot without Improved Regeneration Stacks:
http://imgur.com/HcITquj
Second Screenshot with Improved Regeneration Stacks:
http://imgur.com/0Sjo616
status changed from new report to report confirmed
status changed from report confirmed to fix need test
Assigned to Lynix
Maybe the druid cm who put this report in confirmed, should actually test the spell to see if it's fixed. It has been 3 weeks now and no test has been done.