Nominally, F90T files which do not contain templates, usage of STL classes, etc. are not written to F90 files. This makes it difficult to use advanced Fortran features such as enumerations.
This is related to the feature request to mitigate the parsing of the STL.
Workarounds exist for this:
1) Simply put use_String at the top of your file and maybe declare a type (String) or two.
2) Use the --templates='' flag to indicate a blank string of templates.
3) Use the --template_dir="IGNORE" to ignore templates.
This is fixed now. PyF95++ writes all preprocessed files that are provided in the --sources flag and those in --src_dir.