"abl. sing. only pinu; gen. and abl. plur. pinorum and pinis)", but then it goes on to cite the accusative plural pinos in Virgil. And that note implies a strict distinction between dative plural pinibus and ablative pinis, which seems weird. Not that the rest of it isn't weird, I guess.

(As an aside, the note for quercus that "dat. and abl. plural do not occur"... I can believe that a lack of genitive and dative forms for vis is a fact about the language. Dative and ablative plural forms existing for pine trees, but not oak trees, feels more like a coincidence of the historical record than a fact about the language.)

No, I'm not sure. See the sibling subthread. They're not less weird in the fourth declension, which is itself overwhelmingly masculine or neuter.

That said, second declension forms do seem to be attested for nearly every case of pinus.