advice on storing an impersonated credential

[Martin Gee]

I'm attempting to gss_store_cred an impersonated credential so I can acquire it later.  This does store the cred in the cache. I can see it with klist. 
After I store it, I try and acquire it with gss_acquire_cred_impersonate_name.  It fails with Credential usage type is unknown.
I'm using the latest kerb build. I believe this used to work with 10.1.13