I can reproducibly generate the failure

    mergeConflictingNons failed in geteff with ix

by pulling a patch from my make branch to unstable, recording a
conflict resolution, then trying to pull the remaining patches.

    $ darcs get --lazy http://twb.ath.cx/darcs-unstable
    $ echo yd | darcs pull --repodir darcs-unstable http://twb.ath.cx/darcs-make
    $ darcs record -am x --no-test --repodir darcs-unstable
    $ darcs pull --all --repodir darcs-unstable http://twb.ath.cx/darcs-make

    darcs: mergeConflictingNons failed in geteff with ix
    {{
    |hunk ./GNUmakefile 39
    |+                ./src/Darcs/SlurpDirectory\
    |conflictor [
    |hunk ./GNUmakefile 39
    |+                ./src/Darcs/SlurpDirectory\
    |]
    ||:
    |hunk ./GNUmakefile 35
    |-SRC_DIRS:=. ./src ./src/Crypt\
    |-                ./src/Darcs\
    |-                ./src/Darcs/Commands\
    |-                ./src/Darcs/Repository\
    |-                ./src/Darcs/Patch\
    |-                ./src/win32\
    |-                ./src/win32/System\
    |-                ./src/win32/System/Posix\
    |+SRC_DIRS := . $(shell find src/ -name sys -prune -o -type d -print)
    |:
    hunk ./GNUmakefile 35
    -SRC_DIRS:=. ./src ./src/Crypt\
    -                 ./src/Darcs\
    -                 ./src/Darcs/Commands\
    -                 ./src/Darcs/Repository\
    -                 ./src/Darcs/Patch\
    -                 ./src/win32\
    -                 ./src/win32/System\
    -                 ./src/win32/System/Posix\
    +SRC_DIRS := . $(shell find src/ -name sys -prune -o -type d -print)
    |hunk ./GNUmakefile 35
    |-SRC_DIRS:=. ./src ./src/Crypt\
    |-                ./src/Darcs\
    |-                ./src/Darcs/Commands\
    |-                ./src/Darcs/Repository\
    |-                ./src/Darcs/Patch\
    |-                ./src/win32\
    |-                ./src/win32/System\
    |-                ./src/win32/System/Posix\
    |+SRC_DIRS := . $(shell find src/ -name sys -prune -o -type d -print)
    |:
    hunk ./GNUmakefile 35
    -SRC_DIRS := . $(shell find src/ -name sys -prune -o -type d -print)
    -
    |:
    hunk ./GNUmakefile 39
    +                 ./src/Darcs/SlurpDirectory\
    |:
    hunk ./GNUmakefile 35
    -SRC_DIRS:=. ./src ./src/Crypt\
    -                 ./src/Darcs\
    -                 ./src/Darcs/Commands\
    -                 ./src/Darcs/Repository\
    -                 ./src/Darcs/Patch\
    -                 ./src/win32\
    -                 ./src/win32/System\
    -                 ./src/win32/System/Posix\
    +SRC_DIRS := . $(shell find src/ -name sys -prune -o -type d -print)
    }}
    xx
    hunk ./GNUmakefile 35
    -SRC_DIRS:=. ./src ./src/Crypt\
    -                 ./src/Darcs\
    -                 ./src/Darcs/Commands\
    -                 ./src/Darcs/Repository\
    -                 ./src/Darcs/Patch\
    -                 ./src/win32\
    -                 ./src/win32/System\
    -                 ./src/win32/System/Posix\
    +v v v v v v v
    +*************
    +SRC_DIRS := . $(shell find src/ -name sys -prune -o -type d -print)

I believe this is also resolved by

* resolve issue1043: avoid use of sort_coalesceFL in Patch.Real.               
                                                      
Ignore-this: 79003144c8571ef746108e09192cb4ed                                  
                                                      
The trouble was that sort_coalesceFL does the "coalescing" which isn't         
                                                      
governed by strict rules.  This might have been fixed by changing              
                                                      
sort_coalesceFL to also run canonize, but the cleaner solution is to           
                                                      
simply acknowledge that what I really wanted was just to join together         
                                                      
pairs of inverses, which is much easier than the problem                       
                                                      
sort_coalesceFL is trying to solve.