I got some issues retrieving binary attachments via the REST2-API. It seems like the API tries to escape the several symbols in the file as unicode literals. To replicate this upload a binary file (e.g. some .exe) as attachment in an rt5 ticket and try to retrieve it via /REST/2.0/attachment/attachment id. You will see what I mean.
If I download it via REST 1 (/REST/1.0/attachment/attachment_id/content) it works. It also works downloading the file via gui.
I don’t think that this is intended.