As part of Bug 833158, the dependency should be unslotted. Furthermore, I'm not sure if it was intended, but the latest unstable version of media-libs/openexr:0 is newer than media-libs/openexr:3. Reproducible: Always
Unmasking keyword for 'media-libs/openexr' pulls in slot 0, which resolves the issue with the target location of /usr/include/OpenEXR.