It seems --boring does not work at all if a boringfile has been added:

ben@sarun[1]: .../tmp/bb > darcs --version
2.5.2 (release)
ben@sarun[1]: .../tmp/bb > darcs initialize
ben@sarun[1]: .../tmp/bb > echo '^bin($|/)' > .boring
ben@sarun[1]: .../tmp/bb > darcs setpref boringfile .boring
Changing value of boringfile from '' to '.boring'
ben@sarun[1]: .../tmp/bb > mkdir bin
ben@sarun[1]: .../tmp/bb > touch bin/test
ben@sarun[1]: .../tmp/bb > darcs whatsnew
changepref boringfile

.boring
ben@sarun[1]: .../tmp/bb > darcs record -l
addfile ./.boring
Shall I record this change? (1/3)  [ynW...], or ? for more options: y
hunk ./.boring 1
+^bin($|/)
Shall I record this change? (2/3)  [ynW...], or ? for more options: y
changepref boringfile

.boring
Shall I record this change? (3/3)  [ynW...], or ? for more options: y
What is the patch name? added .boring and set as boringfile
Do you want to add a long comment? [yn]n
Finished recording patch 'added .boring and set as boringfile'
ben@sarun[1]: .../tmp/bb > darcs whatsnew
No changes!
ben@sarun[1]: .../tmp/bb > darcs whatsnew --boring
No changes!
ben@sarun[1]: .../tmp/bb > darcs whatsnew --no-boring
No changes!
ben@sarun[1]: .../tmp/bb > ll  
total 8
drwxr-xr-x 6 ben ben 4096 Mar 29 00:17 _darcs
drwxr-xr-x 2 ben ben 4096 Mar 29 00:16 bin
ben@sarun[1]: .../tmp/bb > ll bin
total 12
-rw-r--r-- 1 ben ben 0 Mar 29 00:16 test
ben@sarun[1]: .../tmp/bb > darcs whatsnew -l --no-boring
No changes!
ben@sarun[1]: .../tmp/bb > darcs whatsnew -l --boring   
No changes!
ben@sarun[1]: .../tmp/bb > echo '^xxx$' >> .boring
ben@sarun[1]: .../tmp/bb > touch xxx
ben@sarun[1]: .../tmp/bb > darcs whatsnew -l --boring
M ./.boring +1
ben@sarun[1]: .../tmp/bb > darcs whatsnew --boring
hunk ./.boring 2
+^xxx$

probably minimal test, using the default boring file:

# cd $(mktemp -d)
# darcs init
# touch core
# darcs whatsnew -l --boring
No changes!

expected behaviour: (simulated by doing  rm _darcs/prefs/boring  first)
# darcs whatsnew -l --boring
a ./core

version: I tried  darcs 2.5.1

P.S. The real use case I had was to implement an analogue of 'git clean'
via 'darcs whatsnew -l --no-summary --boring', 'sed', 'xargs' and 'rm'.
In the particular scenario I tried (ghc repository) it would actually be
helpful to be able to provide an alternate .boring file for a single
command (which would, in this case, contain a list of all the
"subrepositories" inside the ghc source tree.)

My use case was to actually disable the boringfile, because I wanted to
check that my build tree was clean (I usually modify the boringfile to
ignore files and directories that are built during make).

This issue is supposed to be resolved by this patch:

"Resolve issue2054: option --boring does not work with self-made 
boringfile"

This actually seems to be a duplicate of issue1332, so I won't bother with 
adding a test. Still fixed in HEAD, in any case!

The following patch sent by Scott Lawrence <bytbox@gmail.com> updated issue issue2054 with
status=resolved;resolvedin=2.8.0 HEAD

* Resolve issue2054: option --boring does not work with self-made boringfile 
Ignore-this: 5dccf05526201c981c6a76f96de5e044