In case anyone is still looking for an answer, hopefully this will help out. All our S4,s, S5's and S6's had the same issue but only for the built-in AS client and only for those running Lollipop. So I did some testing and found something interesting:
The old set-activesyncmailboxpolicy is deprecated in our up-to-date E2013 servers. That command set the size as a straightforward number of KB i.e. a plain number with no qualifier. However, it appears the policy format has changed along with the editing command and it now takes a size qualifier of GB, MB or KB, with unqualified numbers now meaning plain Bytes. That suggests that the AS client in Lollipop is actually being quite strict as to how to read the new style, whereas Touchdown and Outlook clients seem to assume that unqualified numbers = KB as before.
So it's not really a bug, rather MS not thinking about backward compatibility as hard as they should have (how tough would it be to allow a B qualifier and assume unqualified was KB on all AS policies?). So all you need to do to 'fix' the issue you need to edit all your activesync policies with the new command and make sure to use an appropriate size qualifier. Btw - I've no idea if this applies to older versions of Exchange.
Example (for the Default policy - rinse & repeat for any additional ones):
set-mobiledevicemailboxpolicy -Identity Default -MaxEmailBodyTruncationSize 200KB -MaxEmailHTMLBodyTruncationSize 200KB