Pull Request build failed

I am building a android project from bitbucket and i am having trouble with pull request builds.
Regular builds started by a push to master just work fine, but it looks like builds started from pull requests use a completely different task list.

docker image: circleci/android:api-23-alpha

Task list of a reqular build
Spin up Environment
Checkout code
chmod permissions <- custom task (u+x gradlew)
Restoring Cache
Download Dependencies
Saving Cache
run lint test <- custom task
Uploading artifacts
Uploading test results
Uploading test results
gradle build <- custom task
Uploading artifacts

Task list of failed PullRequest build:
Starting the build
Start container
Enable SSH

Restore source cache
Checkout using deploy key: XXXXX

Configure the build
Exporting env vars from project settings
Restore cache

gradle dependencies <- this task failes (because gradlew is not executable)

Collect test metadata
Disable SSH