calculus and analysis - Are greek symbols causing different evaluation?

I've updated today to Mathematica 9.0.1.0 from version 8 and found something that absolutely confuses me.
Let us define a piecewise function:

gr[x_, v1_, v2_, v3_, v4_, v5_] = 
Piecewise[{{g, v1 < x < v1+v2}, {g, v1+v3 < x < v1+v2+v3}, 
{gs, v1+v2+v3+v4 < x < v1+v3+v2+v4+v5}}, 0]

and try integrating it with obvious assumptions:

Integrate[gr[x, a, b, c, d, e], {x, 0, END}, 
Assumptions -> {0 < a < a+b < a+c < a+b+c < a+b+c+d < a+b+c+d+e < END}]

This takes around 60 seconds and obviously results in 2 b g + e gs (although it seems it was a lot faster in Mathematica 8, though it's not the point here). Now, if we do the very same integration, but with different symbols:

Integrate[gr[x, τ, δ, Δ, τs, δs], {x, 0, TR}, 

Assumptions -> {0 < τ < τ+δ < τ+Δ < τ+δ+Δ < τ+δ+Δ+τs < τ+δ+Δ+τs+δs < TR}]

All of a sudden this doesn't evaluate in 60 seconds, running till it pages all the memory available and crashing afterwads. Can anyone explain this?