I don't think it is STI per se. OP, are you talking about trigger shifters that are attached to the brake lever? There should still be a distinct lever for each: brake, upshift, downshift. With Shimano STI, the brake and downshift (right-side) levers are combined.

You did not mention whether you adjusted the rear derailleur after re-installation. Changing the rear wheel may have slightly changed the distance between the cassette and the dropout/rear derailleur, requiring you to adjust the limit screws and cable tension.