When deleting and recreating a poll, old options aren't deleted and reappear with the new ones

Steps to reproduce:
1) Create a new thread with a poll in it, with the answers "A" and "B", and save the changes.
2) Edit the thread, delete the contents of the textarea where the answers are, and save the changes.
3) Edit the thread again and add a poll, but this time with answers "C" and "D".

Expected:

• Only "C" and "D" should appear as answers, since "A" and "B" were deleted.

What it happens instead:

• The four answers, "A", "B", "C" and "D" appear in the poll. Furthermore, if you vote "A", it will count a vote for "B" too, even if its a one-answer poll. The same when voting "C" or "D".

I tested with 3.0.5 and a clean install of 3.0.7-PL1. Both behave the same.