last reply doesn't appear at the end of the topic

[NeXuM]

I have a weird bug on many of my forums, and i have no idea where it comes from.

If i reply to a message that was posted a few minutes ago, sometimes the post will not appear at the end of the topic. The reply will appear BEFORE the preceding post


let's say time is currently 12h30 and my topic looks like this

12h00 - topic
first post of the topic

12h15 - first reply
first reply of the topic

12h28 - last reply
this is the last reply of the topic, posted at 12h28

now let's say i post a reply to this topic. The time is currently 12h30, so the post should appear AFTER the "last reply"

but the reply will be displayed in wrong order, like this:

12h00 - topic
first post of the topic

12h15 - first reply
first reply of the topic

12h27 - the new reply i just posted
this is a reply i have just posted, it should appear at the end of the topic

12h28 - last reply
this is the last reply of the topic, posted at 12h28

notice how my last reply appear BEFORE the last post of the topic, AND the time of the post is also incorrect ?


i'm not sure if this bug is related to vbulletin because i also have the exact same bug with phpBB

i use vBulletin 3.6.4
and i have the same bug on phpBB 3.0.6 (last version)

The bugs seems to have appeared since my forums got a lot of posts and a rise of activity


I have the same problem on various websites:
http://www.pirate-punk.net
http://www.anarcho-punk.net
http://forums.resistance.tk

any idea where it can comes from ?