QKeyValueIterator<K&,V&> defines some STL-compatibility nested typedefs:

using value_type = std::pair<K&,V&>;
using reference = const value_type &;

QKeyValueIterator::operator* return type is value_type.

std::reverse_iterator::operator* return type is reference.

Therefore, if a QKeyValueIterator is wrapped in a reverse_iterator, then reverse_iterator::operator* will return a dangling reference to the temporary object returned by QKeyValueIterator::operator*.

A possible solution would be to change the definition of reference:

using reference = value_type;

This would be consistent with the STL principle that the reference typedef doesn't actually need to be a reference type, if it is a proxy type that can behave like a reference.