List of steps to reproduce (step by step, including full links if applicable):

The use of %%basaepagename%% as a string does not replicate the mediawiki behavior for {{BASEPAGENAME}}. The mediawiki behaviour that AWB variable replicates is {{ROOTPAGENAME}}. Only really noticeable when you get to a third level subpages and beyond.

Tried to explain it at AWB talk though seems it wasn't the clearest possible

The "official test" shows the same thing, though

What happens?:

https://en.wikisource.org/wiki/Patient_Protection_and_Affordable_Care_Act/Title_I/Subtitle_D/Part_IV

{{PAGENAME}}
Patient Protection and Affordable Care Act/Title I/Subtitle D/Part IV

%%basepagename%%  
Patient Protection and Affordable Care Act

equals {{ROOTPAGENAME}}

What should have happened instead?:

https://en.wikisource.org/wiki/Patient_Protection_and_Affordable_Care_Act/Title_I/Subtitle_D/Part_IV

{{PAGENAME}}
Patient Protection and Affordable Care Act/Title I/Subtitle D/Part IV

{{BASEPAGENAME}}
Patient Protection and Affordable Care Act/Title I/Subtitle D

Software version (if not a Wikimedia wiki), browser information, screenshots, other information, etc:

AWB v 6.2.1.0