reserving hero buttons

how does the reserve hero buttons function work? i tried reserving 6 then adding 5 unit abilities to a paladin, and when i testmapped he only had one spot open for a hero ability -- the unit abilities took over i guess b/c they were there first, even though i told it to reserve spots.

what i'd like to do is be able to add abilities that are pushed off, to give the hero bonuses. but if they took hero ability slots because that ability wasn't learned yet, that'd ruin it.

one workaround would be to give heroes an extra level of all spells, then start them off with a level in everything (which does 0 damage or costs 99999 mana or whatever on the first junk level). but this seems silly.

I am unsure since I never used it, but I think reserve hero buttons refers to the pictures of your heroes you get on the left of the screen.

oh! that makes sense. thanks.