Strange Behaviour in RAP Managed with Draft functionalty

[#1]

I have developed RAP Managed application with Draft functionality. And in my BD, I have mandatory field check on a key field say 'OrderNo' during create and Read only during Update something like below.

field ( mandatory : create, readonly : update ) OrderNo;

Now when I try create, it doesnt take me to the create page. It gives mandatory field error even before navigating to create Page. The error is as follows

At create the mandatory element 'ORDERNO' of entity 'zc_ord1' was not provided

Now However this issue is not applicable for non-draft Application.

Q1> if this happens, this should happen both for draft and non-draft.

Q2> I have not written a single line for Validation. In fact there is no validation. Then where this message is coming from. Is this from standard framework. If yes then why I dont get message in a non-draft functionality if I miss mandatory field

[junwu]

I guess there is no odata call for creation for nondraft when you click create button