Follow status/button doesn't update correctly when posting a comment

There are 2 different bugs for this function.

Here are the steps to reproduce the issue:

1. Create a new topic WITHOUT following it.

2. Now reply to the topic after enabling the Follow topic option

At this point, you’ll notice 2 different things depending on whether auto-merge is enabled or not:

1. If auto-merge kicks in => The comment is merged into the previous post, but the FOLLOW status is NOT updated. Even if the replies are merged, it should still add me to the topic’s following list.

2. If auto-merge is disabled (or doesn’t kick in) => The comment is posted correctly, and I am added to the following list for the topic, but the follow button at the top of the page doesn’t update to show the change like in v4. I must refresh the page to verify I am indeed following the topic now.