I suggest taking a look at your html sanitization settings make sure html isn't allowed in markdown settings.
Next step would be to move the other 2 topics from that category and check if you still see broken markup.
I checked the database and found that pid reserve the IP address of that post as well, however posts.ip obviously does not return that string value.
So I assume that there are codes in which determining function .user.postcount to return an integer right? Can anyone tell me that where could I find those codes, So that I can write some similar function to return the IP address？
We do return the ip but only for admins and mods.
post.ip = topicPrivileges.isAdminOrMod ? post.ip : undefined; take a look here
Keep in mind IP tracking needs to be turned on in the ACP for this to work.