hi mihai;
are you directly connecting port to led?any series resistor?if there is no series resistor it means that at the same time the internal transistor has to sink a lot of current and keep its voltage about 3v
(led=2v approx.).now a current can't flow
in this case and pin shall be pulled high.
try putting a resistor if u havent done so.if u have done so try some buffer.
pranav