ghci and ghc-pkg disagree about what's exposed

I have installed vector-0.10.12.3 and vector-0.11.0.0. At some point, I had hidden both from the package database; however, I later used ghc-pkg expose to mark one as visible again. Now I seem to be in a strange state where ghci and ghc-pkg disagree about what is hidden:

% ghci-7.10.2     
GHCi, version 7.10.2: http://www.haskell.org/ghc/  :? for help
Prelude> :m +Data.Vector.Unboxed

<no location info>:
    Could not find module ‘Data.Vector.Unboxed’
    It is a member of the hidden package ‘vector-0.11.0.0@vecto_3jMaUrldidp1bqsrn0qsS2’.
    It is a member of the hidden package ‘vector-0.10.12.3@vecto_1COyUuV1LrA1IjYnWfJnbs’.
Prelude> 
Leaving GHCi.
% ghc-pkg-7.10.2 list vector | cat
/usr/local/lib/ghc-7.10.2/package.conf.d:
    (no packages)
/home/dmwit/.ghc/x86_64-linux-7.10.2/package.conf.d:
    vector-0.10.12.3
    (vector-0.11.0.0)

% ghc-pkg-7.10.2 describe vector-0.10.12.3 | grep 'key:\|exposed:'
key: vecto_1COyUuV1LrA1IjYnWfJnbs
exposed: True

I have tried reproducing this with other packages in a handful of ways and failed; so I can't give instructions for reproducing. But I am happy to perform any diagnostics you can think of.

Trac metadata

Trac field	Value
Version	7.10.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Package system
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture