ESS Benefits Generic Enrollment - Different behavior backend v/s portal

Question

We are using the ESS Benefits generic enrollment service for enrollment kicking off the adjustment reasons on IT 0378.
Here is the configuration set up, trying to simplify to explain the matter. We are on ECC 6.0 with EHP2.
1.  Configured one plan type in savings category.
2.  Within this plan type,  configured 2 plans.
3.  Configured all other related configuration to set up the 2 plans.
4. Configured the adjustment reason and the appropriate plan type created in step 2.
5.  Created the required adjustment reason on 378.
In HRBEN0001 transaction via backendwe can  see the 2 plans configured within the plan type.
But when Trying to enroll from ESS - only one plan can be seen for that plan type, the other plan is not shown at all.
OK - eventually, debugged and found this piece of code in FM HR_BEN_ESS_FILL_SELECTION_DISP.  The 2 different plans are there until this piece of code takes one of them Off...
  CODE -
3.) Reduce entries to one entry per type and period
  delete adjacent duplicates from selection_display_gt
    comparing pernr
              barea
              bpcat
              pltyp
              begda
              sprps.
CODE -
This FM is called only for ESS application and not for backed program.
What we do not understand is why is it behaving differntly on backend v/s portal.
Any information or experience with this form any one of you will be highly appreciated.
Thanks.

Answer 1

Siddharth,
Thanks for your reply. Yes ESS has its own FMs.  The UI, user exits, BADIs etc are different for backend v/s front end.
What we are not clear with, is the different behavior in core functionality --  i.e. When the adjustment reason is processed from the backend using HRBEN0001 - The 2 plans within the Plan Type are available for elections. BUT the same adjustment reason for the same penr when processed from  ESS - there is just one plan available for elections.
It's clear from the code, that it is deleting one plan and this code is within the FM which is called only from ESS.  But we are still not sure why it should behave differently i.e. 2 plans via backend v/s one plan  via ESS. 
Wanted to see if anyone can share any information if they have a similar benefits set up .. 2 plans within one plan type FOR savings plan category and then having a adjustment reason set up.
Regards.