Using only OC0B pin to generate tone
Possibly relevant: The datasheet p.102 has this to say:

Setting the COM0A1:0 bits to one allows the OC0A pin to toggle on Compare Matches if the WGM02 bit is set. This option is not available for the OC0B pin (see Table 14-6 on page 107).

Might be the issue? (though I haven't looked at Table 14.6)