In the current NEM API, MultiSig transactions store the details of the underlying transfer in a different part of the transaction object than regular transfer transactions.
And because XEM can be transferred as a mosaic as well as a payment, it adds an extra hurdle for anyone wishing to provide services as there are potentially TWO places in a transaction object where the transfer data can be, and two ways of reporting total XEM in the transfer.
This causes problems like this and makes NEM more complicated to support for exchanges and apps.
it would be good if, under Catapult API, the transaction object had a single normalised data structure that summarised the total XEM being transferred, regardless of the transaction type and how the XEM were attached, rather than leaving it to the application to deal with he complexities of transaction types and attachment methods.
Cheers
Rob