Timer interrupt fires just after initialization

[Art-ut-Kia]

issue description: After initializing Timer1 as follows ...

... I observe that the first interrupt fires immediately, while I expected it to occure after 3 seconds.
After a glance into the library code, it seems that the overflow flag (TOV1) isn't cleared as explained here:
https://arduino.stackexchange.com/questions/47265/timer1-firing-immediately

board: Arduino UNO

Complement: I even observe sometimes that several (one or two) spurious interrupts occurs just after initialization of Timer1, afterwhat following interrupts are properly spaced by 3 second intervals.