Github and ghprb don't seem to work in harmony

[Puneeth-n]

I have a jenkins job that runs when code is pushed to master and develop branch. This job also picks up PRs. This job also has sha1 as a build parameter to trigger builds manually.

The job picks up PRs and builds them. Same with pushes to master or develop. The issue is when The job is triggered manually. It seems to pickup a random branch. sometimes a PR, sometimes origin/develop.

Job config

build parameters: sha1 (default value: origin/<branchName>)
Branches to build: origin/master
Branches to build: origin/develop
Branches to build: origin/${sha1}
- [√ ]  Build when a change is pushed to GitHub
- [√ ]  GitHub Pull Request Builder

Jenkins and plugin versions

jenkins version: 2.7.1

Git client plugin: 2.0.0    
Git plugin: 3.0.0
GitHub API Plugin: 1.77 
GitHub plugin: 1.21.1
GitHub Pull Request Builder: 1.33.1