Datasheet

If a write is performed to any of the five timer/counter2 registers while its update busy flag is set, the
updated value might get corrupted and cause an unintentional interrupt to occur.
Related Links
13.9 Timer/Counter Oscillator
ATmega48A/88A/168A
8-bit Timer/Counter2 (TC2) with PWM and A...
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Datasheet Complete
DS40002007A-page 224