I'm not too happy with that compiler indeed.
Ok, well here is something that could be the cause of a lot of other problems.

This one is called on timer1 overflow and it runs, because i see the P0_0 and P0_1 changing.
The only thing is, it seems to 'forget' to increase teller2 sometimes.

The main will be in a while(1) loop, in wich teller2 is only made 0 if teller2>200.
So Knipper should be executed for 100 times, and then 'stops' for 100 times.
The thing is...it doesn't stop


void Knipper(void)
{
teller2++;
if (teller2<100)
{
TR0=1;
teller=0;
EX1=ENABLE; //Extern interrupt enabled
IT1=ENABLE; //interrupt flanktriggered
P1_6=1;
P1_7=1;
P0_1=0;
P0_0=0;
}
}