prepare-commit-msg hook no longer run for cherry-pick?

Hi,

I had prepare-commit-msg hook that would scrub "Patchwork-ID: NNNN" tags form commit messages and would update input mailing list patchwork to mark corresponding patches as "accepted" when I cherry pick form WIP/review queue into branches that I publish, but that recently stopped working if I do a simple cherry-pick. If I specify that I want to edit the message, then the hook is executed:

dtor@dtor-ws:~/kernel/master (for-linus)$ GIT_TRACE=2 git cherry-pick ff162c1554efe951ba6c7a19a228fc76a91fe1ed    
10:43:12.832426 git.c:344               trace: built-in: git 'cherry-pick' 'ff162c1554efe951ba6c7a19a228fc76a91fe1ed'
[for-linus 48bc600a3659] Input: raydium_i2c_ts - include hardware version in firmware name
Author: Jeffrey Lin <jeffrey.lin@rad-ic.com>
Date: Thu Jan 4 21:35:23 2018 -0800
1 file changed, 12 insertions(+), 2 deletions(-)
dtor@dtor-ws:~/kernel/master (for-linus)$ gti reset --hard HEAD^            
HEAD is now at 02a0d9216d4d Input: xen-kbdfront - do not advertise multi-touch pressure support
dtor@dtor-ws:~/kernel/master (for-linus)$ GIT_TRACE=2 git cherry-pick -e ff162c1554efe951ba6c7a19a228fc76a91fe1ed
10:43:24.433162 git.c:344               trace: built-in: git 'cherry-pick' '-e' 'ff162c1554efe951ba6c7a19a228fc76a91fe1ed'
10:43:24.782355 run-command.c:627       trace: run_command: 'commit' '-n' '-e'
10:43:24.786460 git.c:344               trace: built-in: git 'commit' '-n' '-e'
10:43:25.082164 run-command.c:627       trace: run_command: '.git/hooks/prepare-commit-msg' '.git/COMMIT_EDITMSG' 'merge'
hint: Waiting for your editor to close the file...
10:43:31.491551 run-command.c:627       trace: run_command: 'vim' '/usr/local/goo gle/home/dtor/kernel/master/.git/COMMIT_EDITMSG'
[for-linus 039c57df0ec8] Input: raydium_i2c_ts - include hardware version in firmware name
Author: Jeffrey Lin <jeffrey.lin@rad-ic.com>
Date: Thu Jan 4 21:35:23 2018 -0800
1 file changed, 12 insertions(+), 2 deletions(-)
dtor@dtor-ws:~/kernel/master (for-linus)$

Also note that the argument to the hook is "merge" whereas I think it used to be "cherry-pick" earlier.

Is this behavior intentional? dpkg reports version as 2.16.0~rc0+next.

Thanks!