Logging into a Geo Secondary does not redirect to the Primary

When logging into a Geo secondary, the usual and correct flow of events are:

graph TD
    A["1. Visit Secondary"]
    A-->B[2. Logged in on Secondary?]

    B-->C[3. No, redirect to Primary]
    C-->D[4. Logged in on Primary?]

    D-->E[4.1. Yes]
    E-->F[4.3. Redirect back to Secondary]
    F-->G[5. Request OAuth permission if not already granted]

    D-->H[4.2 No]
    H-->I[4.2.1 Request to log into Primary]
    I-->F

    B-->Z[6. Yes, remain on Secondary]

.

For 12.6.0-pre (d7efcb63287), the above flow is not occurring as attempting to log into the Secondary does not redirect back to the Primary (step 3).

@mkozono and I have witnessed this on our local GDK's but it would be good to see it somewhere else before digging into.