When you filter using a tag you’re not permitted to use, the ‘New Topic’ button is disabled. The 
shows the message “You’re not allowed to create topics in this category”. However, the issue doesn’t lie with the category, but with the tag instead. This might seem obvious if you’re only filtering by the tag. However, if you filter using both a tag and a category (for example, ux and completed (link) ), it can give the impression that you’re not allowed to post topics in the ux category.
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