To report a bug with the new forum software please create a new thread in the Forum Beta Feedback section and select "Bug" from the prefix dropdown. The title of your thread should be a short summary of the bug that you have encountered, the body of your thread should contain the following information:
Which page were you visiting when you encountered this bug?
What can we do to reproduce this bug?
What was the expected outcome of the action that you took?
Screenshots, videos and reproduction steps are all greatly appreciated. Please create one thread for each bug that you encounter, this is so that we can easily keep track of individual bugs and provide feedback / request further information if necessary.
If you have any problems posting on the forum bugs can also be reported via the Curse Support System, create a new ticket with "Minecraft Forum" as the selected website and provide the information relating to the bug.