After clicked the Save as Draft button and do not leave the page.
The validation rules will not work.
For example:
A validation rule is: Invalid when Field.Value > 1000
Input the field value: 1200
Step 1. Clicking Submit button: Validation Error. (work as expected)
Step 2. Clicking Save as Draft. Save successfully. Do not leave the page. (work as expected)
Step 3. Clicking Submit button. User can bypass the validation rules. (Unexpected result)
@Guest I was unable to replicate this behaviour, can you confirm if this is for Nintex List Forms in o365 and you are still seeing this behaviour?