Pre queing problems using an audio spliter

First of all i want to say, my audio mono is turned off in settings

Ok so when i turn pre queuing on the left/right side using an audio splitter hooked up to a master speaker and headphones, you can still hear the pre queud song on the master speakers. It seems to work fine for the headphones where the master is on left and queuing is on right. Hope someone can help me out.

ps. this set up that im using used to work maybe a month ago before the recent update