Hello Rahul,
I agree with Sanjay. May be I can explain how this works further.
As a part of check cycle, duplicate check would be triggered, provided all the configurations are correct. (Duplicate check configurations for data model and CR Type's Step level configurations)
Check cycle could be triggered explicitly by clicking on the check button or it'll be called implicitly on submission. In your second case, it'd be getting triggered implicitly. Which means, duplicate check is already being performed before the submission takes place. You should already get the pop-up before the submission is completed. If not, its a bug. You might have to search for a note.
In the duplicate check framework, cl_usmd_duplicate_check->duplicate_check method, each time it is executed, it'll store the search criteria and the corresponding search results the search provider has given. For a given search criteria, in one session, duplicate check pop-up will be shown only ONCE. From the next time, all that is shown is the warning message.
If you want to see the pop-up again you will have to open the corresponding CR again or change the search criteria.
Further, if you set the configuration at CR step level to 'Always Executed', even the approver can see the duplicate check pop-up without editing any data.
Hope this helps. Please let me know in case you have further queries here.
Thanks and Regards,
Avinash Bolisetty