taking sunrise as the model

Interesting you should bring up sunrise. In my research I hit upon sit/set as another case of a type Þ verb, except in this case they are both irregular and, although sit is largely intransitive and set is largely transitive a hen can either sit or set on her eggs and the sun always sets; it never sits. I'm beginning to think that this correspondence of intransitive/irregular and transitive/regular is either coincidental or something that was added to the language later than Old English. For example, scinan, the OE for shine was always irregular. Also, the irregluar rise, is from OE risan, also irregular, but the regular raise is a Middle English addition from Old Norse and may have been taken as regular because it came in during the time when these old forms were getting lost anyway.