http://www.wowpedia.org/Hotfixes. It doesn't mention any hotfixes involving stampede, except the one about Rabid and the one about the arena bug. it also doesn't mention the supposed october 1st tooltip update, and patches 5.0.5a and 5.0.5b were just small changes that couldn't be hotfixed, no tooltip updates.
i've checked http://www.wowhead.com/news=207261/b...nges-and-icons, which is the very first 5.1 PTR update, which should contain the tooltip changes for the hotfixes spells. neither it, nor the build after, nor any later builds mention it as well.
Stampede is the link for the WowDB tooltip. it still shows 175% at this moment, even with the 5.1 PTR already underway. and yes, this IS the PTR link.
if you guys have some other source outside of the game where this supposed hotfix that nerfed Stampede pets to 25% damage, like a bluepost, a tweet or even a log comparison from Beta to live, then i'd love to hear it, because honestly, you're saying that it got nerfed, but I cannot find a single mention of that nerf.