Are we hitting a cap on percent based buffs?

[Zapix]

this is mind blowing - very frustrating!

but this does not seem to apply to %exp increase.. I seem to rmemeber getting 800 exp from wt4 runs when flly stacked up on exp lix.. while normally i'd get about 400 only.. but this was from testing 2 or 3 seasons ago. anyone can confirm?

The Devs told us before the expansion came out that all the exp elixers stack.