My answer was posted twice, despite the rate-limit for users with less than 125 reputation

Question

In attempting to post an answer, I got a message saying:

Oops! Your answer couldn't be submitted because:

• users with less than 125 reputation can only post answers every 3 minutes; try again later

After approximately 3 minutes had passed (not sure if it was less or more), I pressed the "Post Your Answer" button.

When I refreshed the page, I noticed that my answer was posted twice: once when I pressed the button and another 3 minutes ago (the first time I tried submitting it).

It seems like a bug where either:

• the error message is appearing but the answer is being posted anyway, or
• pressing the "Post Your Answer" button duplicates your answer (one of them in the past, seems less probable)

Edit to answer comments:

• It was not an accidental double click, since the answers I posted are separated one from each other by more than 3 minutes, and the answer that caused the error was on a different stackoverflow question. Read the explanation I added below.
• I posted an answer in one Stack Overflow question, and I tried to post a similar answer in another Stack Overflow question, different from the first one. I then got the error message. So I waited 3 minutes, and pressed the Post Your Answer button again, which caused the duplicated answer in the second question I answered. I then had to delete one of the duplicates.
• Since the subsequent answers (separated by 15 seconds) where on different Stack Overflow questions, I don't think it's a latency issue.

Edit: Steps to reproduce:

1. Look for 2 Stack Overflow questions - mine were related (Question A, Question B)
2. Prepare an answer for each questions, but don't post them (Answer A, Answer B).
3. Post an answer to a Stack Overflow question (Answer A, Question A)
4. Delay (15 seconds)
5. Post an answer to another Stack Overflow question (Answer B, Question B). This answer was pre-written, you shouldn't start typing at this step, but press the button to post your answer.
6. You get the error
7. Delay (3 minutes approximately, may be more, may be less)
8. Click the "Post Your Answer" button for Answer B in Question B
9. You get Answer B posted twice, first in step 5, second in step 8