In DotA1, the order in which Tiny casts his Avalanche+Toss combo doesn't matter, he always gets his bonus damage. Even if you Toss your target at something else and then throw an Avalanche on top of him, the bonus damage still applies.
In Dota2, the combo's bonus damage only applies if you hit Avalanche first, and Toss afterward. Toss first variants do not give you the bonus damage.
I can't say whether this is a bug or intended (quite a few patches ago the DotA1 version also only worked with Avalanche first), but there seems to be a lot of misconceptions surrounding this in the community, so maybe some clarification would be nice.
Repro:
1. Pick Tiny
2. Throw a lvl4 Ava>Toss combo
3. Then throw a lvl4 Toss>Ava combo
Result:
2. will do ~900 damage, just like in Dota1. 3 will do ~600 damage, unlike in Dota1.
Expected:
In Dota1 both combos do ~900 damage, so shouldn't they in Dota2?