I was in a server, mineville. I got disconnected, it said "Bug #665, please report" or something, is this serious?

Thank you for your report!
However, this issue is Invalid.

Unfortunately we don't accept issues related to Featured Servers here on the bug tracker, but please add more details if you think this also affects multiplayer over Realms, LAN, or XBL.

I'd suggest contacting the server owner directly or seeking help on the Minecraft forums.

Quick Links:
📓 Bug Tracker Guidelines – 💬 Community Support – 📧 Mojang Support
📓 Project Summary – ✍️ Feedback and Suggestions – 📖 Game Wiki

Thank you for your report!
However, this issue is Invalid.

Unfortunately we don't accept issues related to Featured Servers here on the bug tracker, but please add more details if you think this also affects multiplayer over Realms, LAN, or XBL.

I'd suggest contacting the server owner directly or seeking help on the Minecraft forums.

Quick Links:
📓 Bug Tracker Guidelines – 💬 Community Support – 📧 Mojang Support
📓 Project Summary – ✍️ Feedback and Suggestions – 📖 Game Wiki