If I understand correctly, the moment "shortSound" is started, the sound from "longSound" should stop playing?
On my machine, the sound from "longSound" keeps playing, even if "shortSound" is executed multiple times (executing "longSound" multiple times also plays those sounds over eachother, even when combined with "shortSound")
Click the wrench icon on VoiceAttack's main window, and on the "General" tab of the VoiceAttack options window click "System info >", then choose "Generate Settings Summary"; Save the file and upload it here.