According to the latest
abi/src/pkg/win/setup/NSISv2/AbiWord.nsi, you have a section group (subsection) as the very first section. This is the trigger for the second known problem described in the first post. Your description also matches the bug symptoms. Simply add an invisible section before the first section group to avoid this bug.
Using the latest from CVS didn't help because you probably didn't recompile makensis.exe. I no longer upload a new version of makensis.exe to CVS for every change. I only upload a new version when I release a new version of NSIS. I intend to remove all executables from CVS once I finish a build system I'm currently working on. The new build system will build the entire NSIS package so it'll be easy to make a complete nightly package.