Thanks! This is sorted.
I had not merged the two files sel2vtk.f90 and sel2vtk_new.f90 because I did experience the
the first but not
the second error that user Cfd bumped in. sel2vtk_new was the solution to the first bug, while merging the two seemed to be the solution to the second issue only. In hindsight, neither of them was fully correct.
In the attached file I have zipped the source code that Clemens aka Konsonaut has edited (thanks for bothering), the executable for Linux and the script used to compile and build it. I only took care of naming these as *_merged to distinguish them from the buggy parents.
Hope this helps future users of sel2vtk.
Giordano