Potassium sulfate as a byproduct of manganese heptoxide synthesis?
The reaction you mentioned shows the formation of manganese heptoxide and potassium bisulfate. But if you alter the stoichiometry of the reaction, i.e. change the moles of the reactant, you will obviously get different products like manganese(II or III)sulfate, manganese oxide, potasium sulfate etc. For this, the reaction conditions should be changed.


$$\ce{2KMnO4 + 2H2SO4 ⟶ Mn2O7 + H2O + 2KHSO4}$$



  Potassium permanganate react with sulfuric acid to produce
  manganese(VII) oxide, potassium bisulfate and water. Potassium
  permanganate - solid. Sulfuric acid - 98% solution. The reaction
  proceeds at room temperature. Impurities: manganese(IV) oxide
  $\ce{MnO2}$(source)



$$\ce{2KMnO4 + H2SO4 → Mn2O7 + K2SO4 + H2O}$$



  Potassium permanganate react with sulfuric acid to produce
  manganese(VII) oxide, potassium sulfate and water.(source)



$$\ce{4KMnO4 + 6H2SO4 → 4MnSO4 + 2K2SO4 + 5O2 + 6H2O}$$



  Potassium permanganate react with sulfuric acid to produce
  manganese(II) sulfate, potassium sulfate, oxygen and water. Sulfuric
  acid - 60% solution. Impurities: ozone $\ce{O3}$.(source)



$$\ce{2KMnO4 + 4H2SO4 -&gt;[70-75°C] Mn2(SO4)3 + K2SO4 + 4H2O + 2O2}$$



  Potassium permanganate react with sulfuric acid to produce
  manganese(III) sulfate, potassium sulfate, water and oxygen. Sulfuric
  acid - 98% solution. This reaction takes place at a temperature of
  70-75°C.(source)