Transaction failed: Balance too low to send value for 3rd pending transaction

[PierreBesson]

On https://polkadotmultisig.com/ I am not able to submit additional multisig transactions if I already have 2 pending transactions on this multisig. The UI shows the below popup and no transaction is sent.

Note that each of the pending transaction are for a different account (Account 1, Account 2, Account 3 in the multisig selector box) although they share the same proxy multisig account.

The issue is confirmed because once the 2 pending transactions have been completed by other signatories, it gets unstuck and I can then submit my 3rd transactions without hitting this issue.