Samba does not prevent storage of multiple values in a single attribute if those values differ in binary, even if they are casewise equal.
That is bug 8929, however there is also the issue that if these are found, the object will be returned twice (once for each case-wise duplicate) unless GUID index mode is in use (where they are correctly suppressed).
We'd be leaning toward WONTFIX, given everyone should now be using GUID indexes?
GUID index mode is essentially compulsory for Samba's primary use case, and LDB is maintained for Samba, so WONTFIX and FIXED all at the same time.
It would in theory be nice to fix for raw LDB some day.