Does not change anything. I removed all sei()/cli().
Without setupisr(); I get something about 0,5 Hz at Pin 1 and nothing at Pin 0
Adding setupisr(); I get about 15 Hz at Pin 1 and about 30 Hz at Pin 0.
Disabling Timer1 gives the expected 30 Hz at Pin 0 and (of course) nothing on Pin 1.