Solution testing bugged...?

I would like to give some feedback about ...

From: https://js.checkio.org/mission/digits-multiplication/solve/

Hello guys,

I am new to programming and I know my hindrances, but I have tested my solution on other instances and it seems to be just fine. However, when being tested here, I keep getting "failed", because according to the test my second run gives 87480 instead of 729. But I have tested it and according to it my program works.

Can you please help me with that? What could be possibly wrong?

Please bear in mind that I am coming from nowhere and might have made a very gross mistake, my bad then.

Cheers and happy coding!