search results incorrect

When I generate the webpages in Robohelp HTML, I click on the Search function and type in words and part words. eg.
administration returns 8 topics
admini returns 0 topics

However, some part words do work
numb return 20 topics
numbe return 20 topics
number return 20 topics

Other problems are
search for "adde" returns and if finds words with "ad" and "adde"

and other searches don't even contain the search word but return topics.

I have tried renaming my <<project>>.chm and<project>.cpd files to <project>.cpd_bak and<project>.chm_bak

Any ideas?