b4 using specified base-commit yet still fails to apply?

Hi,

When I do:

git checkout v6.8-rc1

b4 shazam https://lore.kernel.org/all/20240221194052.927623-1-surenb@google.com/ (local)

I can see it detects the base commit (which is v6.8-rc5+)

 Base: using specified base-commit 39133352cbed6626956d38ed72012f49b0421e7b

but eventually fails to apply something:

Applying: mm: create new codetag references during page splitting
Patch failed at 0019 mm: create new codetag references during page splitting

If I do first

git checkout 39133352cbed6626956d38ed72012f49b0421e7b

then it applies cleanly. Is the base-commit handling buggy?

Thanks,
Vlastimil