Progress Billing Rule - Strange Behaviour

This is just a post for me to remember the strange behavior about the billing rule functionality.

Whenever a progress billing rule is configured, for it to make it automatically calculate the % complete, all the projects till date should be selected in the 'Selected projects' section, with 'Chargeable categories' selected for the project configured in the 'Billing rules' section.

If all the projects till date are not configured then the system does not calculate the % complete automatically and that particular billing rule line is treated as manual progress billing rule line, with user having to define the % complete manually.

Not sure why the system behaves this way, but this is how it behaves as of now. More information to be added, if i get to know the 'WHY' for this behavior.

Please refer to the screenshots below.

Billing rule 76 with project selected in the 'Project' field in the 'Billing rules' section

Billing rules 76 with all the projects till date, selected in the 'Selected projects' in the 'Project' section

Billing rule 75 where all the projects till date, NOT selected in the 'Selected projects' in the 'Project section', hence system treated it as a candidate for 'Manual progress billing rule'

Billing rule 76 where all the projects till date, selected in the 'Selected projects' in the 'Project section', hence system treated it as a candidate for 'Automatic progress billing rule'

Thanks
Sarang