tool/mdoc2man.rb doesn't handle man/rake.1 correctly
Before r48658, rake.1 was in mdoc format, and tool/mdoc2man.rb handled it correctly. In r48658, rake.1 was switched to man format, and tool/mdoc2man.rb doesn't handle it correctly, resulting in a broken manual page. Either tool/rbinstall.rb should be modified not to run tool/mdoc2man.rb on rake.1, or tool/mdoc2man.rb should be improved to handle man format without modification.
Alternatively, r48658 could be reverted, putting rake.1 back in mdoc format, and then rake.1 could be updated to reflect the new options to rake. However, I don't see that as a good option unless the upstream rake developers are open to changing rake.1 manual format from man to mdoc.
Note that this isn't a issue if --with-mantype=doc is passed to ./configure or if ./configure determines that mdoc format is supported.
Any change should probably be backported to 2.2, but not earlier versions, as rake.1 uses mdoc format in earlier versions.