1. Summarise the issue (what were doing, what went wrong?)

I was pulling a patch from beta back to alpha. I believe the patch 
involved was an "alternate reality" patch... an intentional conflict. We 
done some development work, and then had to have it undone in production, 
but still exist in development so we could publish it later. 

The repo is unfortunately not one I can share. I can see from output that 
a nested merger was involved. 

3. What darcs version are you using? (Try: darcs --exact-version)

The released version of darcs 2.8. (Darcs 2.5.2 also failed with a 
similar error when attempting this pull). 

4. What operating system are you running?
 
Ubuntu 10.04.