rurwin,
I am pretty sure the batteries are in parallel (a poor man's 26650) and I don't think they use diode isolation (too much voltage drop) so if you do put one in correctly and the other the wrong way you will definitely damage the batteries but then they say the DNA-40 is protect and don't mention what will happen to the batteries. This is just my opinion nothing I know for sure.
I don't understand why the use of flattop batteries is so popular. If they used button tops like ProVape ProVari does it would solve a lot of potential problems and the use of diodes would be unnecessary because the ProVape design uses a mechanical solution to prevent the batteries from making contact when installed in reverse.
Don't know why the don't consult end users... but then what do we know.