Wrong design documents list in indexing task

Steps to reproduce:

1. Create two development identical development views (dev_test, dev_test2).
2. Publish dev_test.
3. Upload some data to corresponding bucket (I used memcachetest).
4. Wait till automatics indexing is triggered. Ensure that all three design documents are in indexing task (all of them are shown as being indexed in the UI).
5. Delete dev_test2.
6. Upload more data to the bucket.
7. Wait till automatic indexing is triggered again. Even though dev_test2 has been deleted it is still included in design_documents list in task status. And it's correspondingly shown in the UI.

Might be related to 04e3dab1c7a27481d30d763be5868a0d965784a9 commit.