There is an assert in CWalletTx::RelayWalletTransaction that gets hit. All other code paths check fBroadcastTransactions before getting to CWallet::ResendWalletTransactionsBefore except the rpc call resendwalletransactions.
It’s an easy fix, but we just need to decide whether to throw an error or return an empty array of rebroadcasted transaction ids.
Should be fixed for 0.15.