Pull-request stage do checkout with short commit hash

I'm using pact (tool for contract-testing) and variable BITBUCKET_COMMIT in Bitbucket pipelines for define versions of my app.

Faced with different behavior when using "pull-requests" stage. 

Cloning code for "pull-requests" has shortened commit SHA then other stages (branches, default).

Steps to reproduce:

1. Create bitbucket-pipelines.yaml(image: atlassian/default-image:2) with "default" and "pull-request: stage
2. Run stages
3. See Build setup

Example for default stage(SHA = 40 symbols):

Example for pull-request stage (SHA = 11 symbols):

As a result for the same commit, variable BITBUCKET_COMMIT has different values.

Suggestion: do a consistent "pull-requests" stage and take 40 symbols commit hash.