Here's the scenario:

1) User posts a new message. It's the newest message in the category, so the message is sorted to the top of the message topic list - lets say the timestamp for the message is 1/1/2018 @ 12AM
2) Some posts are added after the message (1/2/2018 @ 12AM, 1/3/2018 @ 12AM), the message in "1)" falls down the list for each new post. - now in the 3rd slot behind the 1/2 and 1/3 posts.
3) Another user posts a response to the message in "1)" - the message moves up to the top of the list again. Lets say this response is 1/4/2018 @ 12AM
4) 4 more new posts (1/5, 1/6, 1/7, and 1/8 timestamps - same pattern for year and time)
5) A new response to the first message in "1)" on 1/9. So now the original message moves back to the top.
6) Here's the issue: the user in step "3)" EDITs his/her original post that was done on 1/4/2018. Even though the message was at the top of the list, it seems like the EDIT changes the timestamp of the entire thread to the old date of 1/4/2018 - so the message is moved down past the 4 new posts on 1/5, 1/6, 1/7, and 1/8. Although the last response date is "1/9" for this message, the thread date seems to inherit the date of the "EDIT" which occurred before the last response. This seems to incorrectly affect the thread's sort order in the list of topics.