An option on the General
tab page of .NET Windows Forms and Web Forms Project painters allows
you to choose whether to do a full rebuild or an incremental
build when deploying a .NET project. The default option is incremental.

If the application has not been previously deployed, a full
build is triggered by the PowerBuilder IDE even when the incremental
rebuild option is selected. The incremental rebuild option is also
overridden if you remove the build directory that PowerBuilder generates
from a previous build, or if some of the build files are missing
or damaged in the build directory or its subdirectories.