variants not preserved on upgrade

[Jeremy Huddleston]

I have boost installed as +python26+universal:
$ port installed boost
The following ports are currently installed:
  boost @1.42.0_0+icu+python26+universal (active)

but when upgrading, it's trying to pull in openmpi (which is a variant that conflicts with python26).

$ cat .../.macports.boost.state 
variant: +openmpi
variant: +universal
variant: +icu
variant: +python26


So why is it trying to add +openmpi to the variants when it explicitly conflicts? (yes it's in variants.conf)

Furthermore, the error message I get is not about the conflict.  I am given an arch missing error because openmpi is only -universal.