In my native language (not English) it is customary to use the past tense when speaking of properties and (posthumous) actions of deceased persons.
But in English, I occasionally encounter statements like: "[A. A. Milne] is the father of bookseller Christopher Robin Milne [...]" (from the Wikipedia article on A. A. Milne; my emphasis). Both A. A. Milne and his son are no longer with us, by the way.
Is this standard practice, an idiosyncrasy of certain writers, or simply a common error? In any case, the present tense for dead people mildly irritates me, but perhaps that's unreasonable.