I happened to glance upon my flagging history and I realized that there was an entry missing from the spam section in it. I had marked 6 posts as spam, out of which 4 were deemed helpful and 1 was declined. I'm not sure what happened to the remaining 1 entry and why it is missing from the history summary. Here is a snapshot of the spam section of my flagging history.
Note: I've checked my flagging history completely and there is no spam flag which is still in the active state.