'git repack' and repack.writeBitmaps=true with kept packs

I have some unexpected behavior with 'git repack' on git 2.10.2 and 2.11.0.

$ cat /etc/gitconfig
[pack]
        writeBitmapHashCache = true
[repack]
        writeBitmaps = true
$ touch objects/pack/pack-3841d81123a96cedeb3c1bd7acf7e29bfba26639.keep
$ find objects
objects
objects/pack
objects/pack/pack-3841d81123a96cedeb3c1bd7acf7e29bfba26639.keep
objects/pack/pack-3841d81123a96cedeb3c1bd7acf7e29bfba26639.idx
objects/pack/pack-3841d81123a96cedeb3c1bd7acf7e29bfba26639.bitmap
objects/pack/pack-3841d81123a96cedeb3c1bd7acf7e29bfba26639.pack
objects/info
objects/info/packs
$ git repack -Adfl
Counting objects: 16321, done.
Delta compression using up to 24 threads.
Compressing objects: 100% (16118/16118), done.
Writing objects: 100% (16321/16321), done.
Reusing bitmaps: 110, done.
Selecting bitmap commits: 3257, done.
Building bitmaps: 100% (137/137), done.
Total 16321 (delta 11568), reused 4507 (delta 0)
$ du -sh objects/pack/pack*
100K    objects/pack/pack-3841d81123a96cedeb3c1bd7acf7e29bfba26639.bitmap
524K    objects/pack/pack-3841d81123a96cedeb3c1bd7acf7e29bfba26639.idx
512     objects/pack/pack-3841d81123a96cedeb3c1bd7acf7e29bfba26639.keep
4.3M    objects/pack/pack-3841d81123a96cedeb3c1bd7acf7e29bfba26639.pack
100K    objects/pack/pack-6043151bee7bd61bdae6e3a2ba0f13cd1b0277af.bitmap
524K    objects/pack/pack-6043151bee7bd61bdae6e3a2ba0f13cd1b0277af.idx
5.8M    objects/pack/pack-6043151bee7bd61bdae6e3a2ba0f13cd1b0277af.pack

It seems like it's behaving as though I've provided --pack-kept-objects. In order to ensure the .bitmap is created, it repacks everything, including everything in existing .pack files (not respecting .keep). But then it's not deleting the old .pack file (oddly, respecting .keep).

What I'd expect it to do here is ignore the 'repack.writeBitmaps = true' value if there's a .keep that needs to be respected. Is this not a correct assumption?