Your problem is that the one tag is already the community tag you are posting to (top left which is the primary tag when that is the cas) if you remove the community tag then you get 8 tags below. Community tags are reduced from the overall tags you are left to for you to use. the left seven for you to chose than can be typed at the appropriate area below.
Hope that helps.
Thanks. The problem has now disappeared - it accepts all 8 tags and the other message has disappeared; the layout also changed back, no longer splitting the page for posting and seeing as I post - as it was in the image above. I'm glad.