using transfer to return refund to relayer?

[Amxx]

In ERC20Tornado's implementation, refund is forwarded to the recipient using _recipient.call or, if that fails, returned to the relayer using _relayer.transfer

see:

tornado-core/contracts/ERC20Tornado.sol

Line 46 in a533ad9

_relayer.transfer(_refund);

I believe this will limit the ability of relayers to use smart contract accounts for relayer, which might not be an issue right now, but could be in the future. Any documentation on why this is not done using _relayer.call ?