Just a note to conclude my part of the discussion -
I am certain this is a vendor specific issue for downloading DWI data sets (scalar volume export of T1, T2, etc is fine). I have raised this issue with the NilRead (Hyland is company name) but I have no idea if it will be addressed in the future.
I suspect these enterprise level cloud-based PACS systems will become more popular in the future. Indeed for our organization, end-users outside of Radiology have to use this system (I am in Ophthalmology analyzing visual cortex, so I need to use it).