when use VDD channel in SAADC,does it influence AIN3 channel used as GPIO?

[great-master]

I used VDD channel to detected battery voltage, and the P0.5(AIN3) connect to a LED, But I found that after initialize SAADC, P0.5 cannot control output.

[great-master]

I have found the problem,rosin joint! But the the phenomenon is deceptive!