I've never seen this happen before, but here https://gyazo.com/92a8a54738a81f6799635bf661166e5d it says that oreo's last read date was 'N/A'. He had already posted in the inbox so it's not like he hasn't seen it yet. If it matters, it was in the inbox called 'Posts moved from: Hi', in which posts from a thread were put into a PM.
@ModEdit https://www.ecocitycraft.com/forum/threads/some-forum-changes.140181/ - You can now disable non-staff members from viewing your last read date in a conversation if you have forum gold/lite.
