difference between two URLS and users unable to save documents using custom solutions

Hi

1) In a sharepoint farm three application created on diffrent ports

1) sharepoint-80

2) sharepoint-82

3) sharepoint-83

2) here is AAM settings same for three applications 

3)and for these 3 applications Host names  are entered in DNS server

1)sharepoint -80   dns entry (http://xyz)  2)sharepoint -82   dns entry (http://abc)  

and in for all DNS entrys there is a F5 load balancer  IP configured and 80 port opened in this server

suppose the Domain name of our company is : contoso.gov.local

 in all applications there is a custom wsp solution deployed to  upload and save documents and view documents

all domain users authenticated with contribute permissions , to upload documents , when they browse

they enter this URL in same domain:

if they type http://abc   the sharepoint-82 applications open

here my issue is 

when we save documents using a URL http://abc/_layouts/Scan/scan.aspx

users able to save documents in document library

but 

users use this URL  http://abc.contoso.gov.local.82  users unable to save documents 

what is the diffrence between these two URLS and what is the reason users unable to save documents

adil