Sharepoint and Office Web Apps 2013 - Document Editing

Hi..

I made Web Application Program with only NTML Authentication.

Then I extend "Default Web Application" (URL : http:// appserver1)  to make "Intranet" (URL : http:// sps.abc.com)  with only FBA Authentication.

Last, I configured sps and office web apps  to work together.

Both of them  work well except Editing on Extended Application with Error 8115.

(It happens when I connect to the document library through Extended Web Application - http://sps.abc.com - FBA Auth)

Error : Could not contact WOPI End Point. Error details - "filenotfound url -  http://appserver1/sites/doc/_vti_bin/wopi.ashx/files/ad64e33ef7a0416c81415e5855297f4f?access_token=eyJ0eXAiOiJKV1QiLCJhbGciOiJSUzI1NiIsIng1dCI6ImVJUlNCMVByOENZVXVDOF9WeHY1SWR1WkZISSJ9%2EeyJhdWQiOiJ3b3BpL2xnY2hlbS1hcHBzMjo1MTAwMEAwNTBjY2U0Yy1iNGEzLTQ0MDktYTBiOC1kMWM4NjRiM2QxMWIiLCJpc3MiOiIwMDAwMDAwMy0wMDAwLTBmZjEtY2UwMC0wMDAwMDAwMDAwMDBAMDUwY2NlNGMtYjRhMy00NDXXXXX~~~)

When I check this event, I was wondering why URL transfer to Default Application's (http:// appserver1)... I think it should be Extended's (http:// sps.abc.com) not Default's.

Anyway I added FBA Auth on Default Application as well and It made Editing works.

But still I figured out nothing. Does anybody know about this?