The 'Builder Configuration' screen looks for

• ./webapp/templates/plugins/builder/antBuilderedit.ftl
  which is bundled in the distribution as
• ./webapp/templates/plugins/builder/antBuilderEdit.ftl

I suspect there may be other cases. Incidentally, having been bitten by this kind of thing many, many times over the years, our internal dev policy is to only use lowercase for filenames.

The workaround is to rename the file.