technical question regarding multisig vault

I recently tested bluewallet’s multisig vault feature.

I created a vault using same private key with 3 different passphrases for vault key 1,2, and 3.

I funded the vault with small amount. The balance showed on the vault. At this point I assumed the vault was fully functional. However, it is not. I did test send but it didn’t work. The error message says “can not add duplicate data to array.”

Is it the app bug or I created a “burn” vault ?