Open drain concept in ML51SD1AE nuvoton controller

[SANKETMODHE7028]

Here is my task is to blink LED

I use 4 GPIO pin and 4 led are there.
in these case

1. first line high so LED on and then other 3 lines going to open drain mode.
2. . 2nd line high so LED on then 1st ,3rd,and 4th pin going to open drain mode.
3. 3rd line high so LED on then first 2 and 4th pin going to open drain mode.
4. 4th pin high so LED on then first 3 pin going to open drain mode .

this is 4 cases works fine but one issue is generated . if pin going to open drain mode at that time the voltage 0.5 to 0.7 varrying .
i also checked in push pull , pull down/up mode then also pin having something voltage are there. what i do to avoid these error ?