Darkfall had a couple of issues. The first issue was that no one was using Primalist armor. The second was that stamina regeneration was disabled during sprinting. So it seemed like an obvious combination. Give Primalist robes the ability to boost stamina regeneration, let other armor types see stamina drop a bit faster, and everyone would have a bit more motivation to use robes. Elegant, no?
As it turned out, the resultant regeneration and overall issues led to an immediate rollback and a 40% decrease in stamina consumption across the board, meaning that these issues are all back to the drawing board. An apology was issued for the unintended consequences of the patch, with the team promising to examine the issue in more depth whilst looking for a solution that doesn't lead to this level of fan outcry.
[Thanks to Dengar for the tip!]