[gentoo-science] tachyon-0.98.9-r1 fails to install due to wrong USE flags

Hi,
I try to install [sage-on-gentoo] sage. I come until tachyon.
'emerge tachyon' fails with:

>>> Emerging (3 of 20) media-gfx/tachyon-0.98.9-r1
  * tachyon-0.98.9.tar.gz RMD160 SHA1 SHA256 size ;-) ...               
                                                                        
                                            [ ok ]
  * ERROR: media-gfx/tachyon-0.98.9-r1 failed (setup phase):
  *   tachyon does not support MPI with OpenGL and threads

openmpi was installed with "cxx fortran ipv6 romio threads" USE flags.  
There is no OpenGL USE flag for openmpi:

root@caiman:/root(16)# emerge -pvD openmpi

These are the packages that would be merged, in order:

Calculating dependencies... done!
[ebuild   R    ] sys-cluster/openmpi-1.5.3-r2  USE="cxx fortran ipv6  
romio threads -heterogeneous -infiniband -mpi-threads -pbs -sctp  
-slurm -vt" 0 kB

What should, I do only to remove the threads USE flag from openmpi?  
What could be the consequences if I remove the threads USE flag, e.g.  
for Rmpi?

Regards