For the redox reaction
H2O(l) + 2KMnO4(aq) + H2SO3(aq) yields 2KHMnO4(aq) + H2SO4(aq)
apparently the net ionic equation is
H2O(l) + 2MnO4- + SO3-2 yields 2HMnO4- + SO4-2

I'm not sure why the H2SO3 dissociates since it's a weak acid.

Thanks!

you've got the reaction
H20 + 2 K Mn(VII)o$ + H2S(IV)03 --->2 KH Mn(VI)04 + H2 S(VI)04

Manganese 7 is reduced---> Manganese 6
and sulfer 4 is oxidized to Sulfer 6

you may be absolutely correct that the dissociation
of H2S03 --- HS03- & H+ occurs..
The reaction happens to change the HS03- to H2S04 (a strong acid)
and then it disociates to S04-- & 2 H30 + in aqueous solution.

S03-- will also be in solution just at very low concetrations at any particular moment in time.
Ka HS03 of 5.6 E -8 vs Ka H2S03 of 1.7 e-2.
About 500times less..
While this may seem to be a small number Avrogadro's number is incredibly large.. there is still plenty of S03-- in solution to react.