The layer names of a EXR image must be unique to be saved properly, which is weird, of course, but that is a bug :(
Git commit 8cf4c79fdf96cd24bcf915bf8fce4c1c8f140c70 by Dmitry Kazakov.
Committed on 06/04/2014 at 10:09.
Pushed by dkazakov into branch 'master'.
Fix two user-interaction bugs in multilayer EXR
1) Warn the user that some layer types cannot be saved to the EXR
and will be lost.
2) Ensure that all the layer names in EXR are unique. Otherwise the
layer data will also be lost.
M +104 -11 krita/plugins/formats/exr/exr_converter.cc