Joseph,
The "Go to last page" button always refers to the main report. ( and will therefore assure that the entire report has been processed) . Subreports are not "Aware" of the page count in the main report because subreports are processed before the main report is processed. and information is only passed forward ( from the the subreport to the main ( parent ) report. )
...... and since a sub report can occurr many times in a parent report, which page do you mean as the "Last page" of the subreport?
The only way to "goto the end" of a subreport, is to manually scroll through the report