As to the simplification question Thierry points out, it turns out that nearly all of the Maxima simplification methods yield this (though just sending it to Maxima and back, simplify, doesn't). (I also don't see this in Maxima proper, and I'm investigating this.) These are, of course, simplifications, which might only be valid over certain domains, but I haven't seen one involving an unevaluated integral before so I'm not sure what's going on there.
As to the simplification question Thierry points out, it turns out that nearly all of the Maxima simplification methods yield this (though just sending it to Maxima and back, simplify, doesn't). (I also don't see this in Maxima proper, and I'm investigating this.) These are, of course, simplifications, which might only be valid over certain domains, but I haven't seen one involving an unevaluated integral before so I'm not sure what's going on there.