I think I have just found an error with the directory opcode. With directories up to two letters the files list contains the filenames as they are inside the directory. When a directory has three or more letters, the directory name is included in the filenames.
Sfiles directory "x/", ".wav"
Sfiles2 directory "xyz/", ".wav"
Sfiles2 = xyz/a.wav
I accidentally discovered that by using my m_samplebank opcodes with a proper realworld directory name.
I am running the arch package of Csound version 6.15 (September 7 2020)
Can someone verify that behaviour? Is it to a degree intentional?