PrpPack does not work for MOUL files

I just tried to use PrpPack to extract a MOUL prp file ("Ercana_District_Canyon.prp") and it did not work: After running for about a minute, the application canceled with the following error:
The only file which got created in Ercana_Canyon_PRP is called "[0001].po" and has a size of about 330MiB, MUCH bigger than the prp file (which is about 4,5MiB). Extracting a TPOTS file works great. The same MOUL file can without problems be opened in PageEditor.
(that message should really say which file it tried to open)terminate called after throwing an instance of 'hsFileWriteException'
what(): Error writing to file
Aborted
The only file which got created in Ercana_Canyon_PRP is called "[0001].po" and has a size of about 330MiB, MUCH bigger than the prp file (which is about 4,5MiB). Extracting a TPOTS file works great. The same MOUL file can without problems be opened in PageEditor.