Hi,
the all text search works by using an index.

The algorithm that creates the index first separates the words by spaces
and then puts them in the index. Maybe there is a special treatment of 
whitespace in chinese sentences.

To make life more difficult: there are several index "backends" that 
roundup may by using. You could try using a different one to see if the 
situation changes. E.g. try using xapian.

Best,
Bernhard