qt or stl-style iterator + implicit sharing = unexpected behavior

Consider the attached test program.

A naive user would likely expect the output to be:
3 2
1 2
5
1 2

...as indeed it is when using std::map.

However, with QMap, the output is:
3 2
3 2
3
5 2

I realize this is probably difficult to fix (and the performance cost of doing so might be exorbitant), but it seems like an interesting enough caveat to at least warrant a larger warning in the documentation than the passing remark buried in the container overview page. (Also, the existing warning does not appear to cover that making a copy "invalidates" iterators).