Maybe this is a bug in electurm? It truncates the unseeded signatures, maybe to save on blockchain space? However this is exacly not what we want in this case.
No, in case of a P2WSH (or any other SegWit transaction) it is a consensus rule that mandates the stack to be empty after execution. If you include more signatures they won't be popped so the stack remains un-empty so the verification fails.
If this were P2SH then it would simply be non-standard but at the same time those extra signatures could be anything like random data instead of a valid signature. Which means even if the blockchain contained such a transaction it doesn't mean validity.