Does NSIS not support short filename?

Sorry for my poor English, i am a newbie for NSIS
I used "ReadRegStr" to read a software intall path value from registry(the path uses short filename),then assigned the value to "InstallDir" var and tried to use it to extract my files.
What was surprising was that the files failed to extract to the $INSTDIR.But when i changed the path value from "C:\PROGRA~1\ADVANC~1" to "C:\Program Files\Advanced Registry Tracer",everything just worked perfectly.

So why?

Any helps will be appreciated!

Yes.... read in the DOCS about GetFullPathName

Using a short file name with SetOutPath and File works fine for me. You probably have an error somewhere else in your script. I guess it's because you use ReadRegStr to read into a variable but use this variable in InstallDir before ReadRegStr is even executed. Use StrCpy $INSTDIR "new value" instead of InstallDir.