Adding a Suggested Change during Pull Request review with a code of line starting with a tab gets converted into spaces

Issue Summary

Adding a Suggested Change during Pull Request review with a code of line starting with a tab character gets converted into spaces in Bitbucket 8.0 or older.

This is reproducible on Data Center: (yes) 

Steps to Reproduce

1. Create a Pull Request with a file containing a single line starting with a tab.
2. Start the PR review.
3. Select the whole line.
4. Suggest a change to this line of code
5. Change anything in the text and save. 

Expected Results

The suggested change changes only the text and keeps the tab character.

Actual Results

The suggested change changes the tab character into 4 spaces. 

Workaround

Upgrade to Bitbucket 8.1.0 or newer.