ISPAC deployment removing package password?

Background:
Created an SSIS project in SSDT for Visual Studio 2013 few months ago with a few SSIS packages that have an Oracle connection (user-id, pwd).  Both SSIS project and Packages have  protectionlevel set to "protectsensitivewithPassword". Project and Package passwords are same. This is necessitated by the need  to  preserve oracle username and password.
 Deployed whole project to SSIS Catalog on SQL server 2014  in  DEV through PROD  environments. Scheduled Jobs to execute those packages from catalog and Jobs are running successfully.

problem:
I needed to update couple packages as per changed business needs. Modified package validates and executes fine from
SSDT on my workstation, It works fine when i redeploy whole project to catalog interactively (using deploy wizard).

But things get tricky when i try to deploy ISPAC file to Catalog using deploy_project stored precedure as :

Set @ProjectBinary = (SELECT * FROM OPENROWSET(BULK '$(FolderPath)\project.ispac',SINGLE_BLOB) as BinaryData);
exec catalog.deploy_project @folder_name = @foldername, @project_name = @projectname , 
@project_stream = @ProjectBinary, @operation_id = @operation_id;

Deployment completes successfully, but, Modified Package fails  validation with an erorr "package Failed to decrypt the an encrypted XML node because the password was not specified or not correct. Package load will attempt to continue without encrypted information".

Neither Package nor Project password were changed. what could be causing the issue?
Thanks for your help.

Bhaskar