Cannot add private key or login via CLI

I use GPGTools on Mac OS X 10.10, and have a local keyring. My keypair has subkeys, 1 each for encrypting, signing, and authenticating, but the primary private key has been removed for security reasons.

I generally don't have issues with using a keypair that is set up this way with subkeys.

So on the Keybase website, I had no problem updating my public key, but I get this error when I try to add my private key:

Error: no private key material found after merge

I also cannot log in via the command line client with keybase login:

$ keybase login
Your keybase username or email address: smt
▶ ERROR Bad key found: no private key material or GPGKey

These errors are very similar. Is the inability to use a keypair with no primary private key a known limitation of the OpenPGP lib(s) used by Keybase?

I haven't tried with my master keypair (and don't intend to), so I am not sure if this is even the issue, but it does seem related to some library not being able to detect the private key.

Start by reproducing the keybase login failure and the private-key import error with a keypair whose primary private key is absent but whose subkeys remain. Investigate the OpenPGP library handling behind these entry points and compare the behavior with a complete keypair. Done means confirming whether this key layout is supported and documenting or correcting the resulting behavior.