TIL && guarantees order of execution and doesn't execute right part when not needed.

Fixed

Please which language? To post an issue:

Here are some general guidelines about posts:

Issue: problem in the kata itself (description, wrong tests, wrong internal solution...)
Suggestions: well, that part is clear
Question anything else that is related to you having a problem solving a kata
For information, when you post issues:

provide ALL the useful information:
language
input
outputs (actual expected) when relevant
error message when relevant
check, DOUBLE check that this IS an issue, meaning that the problem is in the kata itself and not in your code. If it's in your code, post rather a question
if you pass this step, you still have to prove/explain what the issue is (and if you can provide fixes, it's even better)

That's true, I just re-used code I already wrote for other arithmetic katas, such as division with remainder, multiplication and square root of large integers.
Then I copied and pasted, and I used the multiplication routine.
Awkward code indeed, but it worked.