I think this has only happened recently, but I may be wrong. Almost any set of words you type into the search box get rejected as “too common”. This makes it especially difficult to search for terms from the Collada spec. A good example is to search for bind_vertex_input. It appears that everything that is non alphabetic is treated as whitespace and bind, vertex, and input are considered too common. I had a quick search on the phpBB web site and it appears that this is a common problem related to use of default values for the “COMMON WORD THRESHOLD” parameter. It appears that you can disable this feature by setting this parameter to zero and deleting and rebuilding the search index. I suggest that this is what should be done.