Nostalrius Begins - Quality wow vanilla realm (1.12)

so i have 3 talents into curse of exhaustion improved and its supposed to increase the slow by 15% so a total of 25% slow instead of 10% but the spell only slows for 10% can anyone help?

Bugs are to be reported on the Bug Tracker, not the forum buddy.

And is just a tooltip bug, or is the actual speed reduction bugged? Cause if you're looking at the debuff on your target, 99% of the time they don't show talents improvements.