Comment # 14 on bug 1208248 from Egbert Eich

Right. Meanwhile I found it. The old (non-arch) update alternatives need to we
wiped before new (arch-dependent) links can be set up for the same path. This
cases the link that's created by 
ln -sf openblas-default/libopenblas.so.0 /usr/lib64/libopenblas.so.0
to be dangling.
The ldconfig at the end of the script takes care of this and wipes it.

I'm presently preparing fix. I will test it before submitting.
I've set up everything so I can test if this works.

Thanks for your help!