Oh it has to be synch, not sync. You can't split a chi down the middle like that.

I feel no urge at all to apply the irregularity of its homophone to a new (and therefore regular verb). I'm sure this says something Pinkerish, such as that exceptions are stored not phonetically but semantically.

The picture was hung, the convict was hanged: it still takes a moment's thought with me; likewise, "still lifes". But basically exceptional forms are stored as individual entries, not as patterns. At an early stage in child development they start making irregular patterns apply to regular words, then later learn to make the correct distinctions. So the existence of two words /siNk/ with different behaviours should be no problem.