I always figured that diocesan priests don't particularly like it when a religious priest becomes the Bishop. I figured that's why John Paul II chose O'Malley to fix the mess in Boston.
Some years later I was studying under a priest-professor who was Provincial Emeritus for his religious order and he says that diocesan priests feel like it's a "downer."
Why is this so? I read an article from John Allen saying that it's because diocesan priests might feel slighted because a Bishop wasn't chosen from within their ranks to lead the Diocese, but that doesn't seem to really answer the question, because in any case aren't Bishops nowadays typically chosen from areas outside of their new sees? Where I am, the current and previous Bishop were both from other dioceses before they were called to lead our diocese. Dolan of New York was from Milwaukee. Tagle of Manila was from Imus. DiLorenzo of Richmond was from Philadelphia and Honolulu. Though I gather historically it wasn't always this way -- Wojtyla was Archbishop of his hometown.
And in any case, at least where I am, the diocesan priests and religious priests get along like brothers. I can't see it being a problem here, though I suppose I could see it becoming an issue in places where they have a lot more priests who may tend to form cliques among themselves divided by orders and seculars?