Yes, I understand.
However, in this case I’m using elastix (elastix.isi.uu.nl), which is a registration software that uses itk. I’m using that program, and not programming it myself. I think I could provide a stripped-down registration example (fake images and registration parameter file) but I certainly will not be able to adapt the code as you suggested.
Main reason for posting was hoping that someone in the itk-community (possibly also with elastix experience) recognizes this problem, or knows what relevant changes have happened in itk when going from 4.8.2 to 4.9.1 (something with multi-threading?) that may have caused this problem.
Best,
Theo