Floating value when connecting to IC input
As brhans mentioned in comments, I believe your IC is 'leaking current' to your input/output lines, with the 1.5V you're seeing being the forward-bias voltage of your diodes.

To fix thks, try connecting a pull-down resistor in parallel to each LED (size according to anticipated leakage current), giving that current a path to ground.

Something like this:

(resize the 10K resistors as appropriate to your leakage current &amp; acceptable 'low' voltage).