自动执行:removeFromSuperview / removeconstr抛出异常并严重崩溃

We use auto layout constraints selectively, primarily to position labels in relation to editable field elements (UITextView, UITextField, typically). However, since implementing auto layout for these fields, we're seeing a nasty exception and crash whenever we're unloading views, deallocating, etc. The exceptions are happening as it's attempting to remove the constraints from a view before unloading it.We use auto layout constraints selectively, pri