I have probably mistakenly txt imported same card on two different occations.
In this cases Mnemosyne accepts the duplicate (see attached hardcopy of browser). And yes, every single cahracter is identical...
The system allows even a "triplicate" (see attached hardcopy of browser _3)
However: When copy number four tries to enter the scene, the duplicate guard is on the alert. (see attached hardcopy of browser _02)