Twice in the past few minutes I've hit the 'Post' button only to be taken to a page telling me "Authentication Ticket Mismatched, failed authentication. Return to my original page"
If I click the provided 'Return...' link it seems to take me to ANOTHER post I had open in another browser tab, instead of back to the post to which I was attempting to reply.
If instead I hit the browser 'back' (chrome restores the typed-in post, thankfully) and hit the submit button again it then posts successfully.
You can open many tabs, but keep in mind that the inactivity time for a given session is 30 minutes. So, if you opened a window and got interrupted by something else, you would see that error message on the tabs that were open for more than 30 minutes. You can reset your session time by either logging back in or clearing cookies and temporary internet files.