vf01 negative balance error and user exit with export parameter = import parameters

[vieet]

Hi Gurus,

I am facing strange scenario and I could not able to understand the issue with tcode VF01.

We were going to automate the INBOUND DELIVERY for our customer. It means whenever vf01 is executed and billing number
gets generated same time specific data(as json)  has to be send to our customer by consuming API.
To do this I have searched for userexits in VF PACKAGE and I have implemented 4 userexits with just breakpoint(code)  in it to check which user exit will hit when I click on save button.
EXIT_SAPLV60B_001
EXIT_SAPLV60B_010
EXIT_SAPLV60B_002
USEREXIT_FILL_VBRK_VBRP

When the functional run the tcode VF01 they were facing negative balance error. They told me that I have made changes in the code and from
then onwards the issue started.

To fix this issue I have simply mapped the import with export parameters inside all the 4 based on the import and export parameters of the respective
userexit after removing the breakpoint.

FUNCTION EXIT_SAPLV60B_001.

FUNCTION EXIT_SAPLV60B_010.

Like the above I have done for others also.

After doing this mapping in all the 4 user exits the error issue got resolved. Now the transaction is running smoothly.

Then I thought that I have unnecessarily implemented 4 userexits which is of no use( by mapping import and export parameters )  as I have not written any meaningful  logic in it.

I have deleted the includes of the user exits (back to square one). Now there is no custom code in the transaction after save button is pushed.

Again the negative balance issue started popping up.

I have implemented the userexits with import and export parameters mapping and the issue is resolved again with no error.

I could not able to understand how the mapping of import and export parameters is fixing the negative balance error.

My understanding is that data flow should not be impacted when I delete the includes of userexits from se38.

This is strange issue and I have debugged alot and I could not able to understand what is happening.

The whole strory which I am trying to explain is only in QAS.

without these user exits the VF01 in PRD is running smoothly. 

Kindly let me know what would be consequences of the active userexits with just map of import to export in QAS and not in PRD ?