I'll try to explain it, so you can reproduce it yourself.
For example, I have a topic "xyz" where user "max" has posted 4 messages. In three of these messages he has used the word "manual". Okay.
I go to the search function and I only check the sub-board where the topic is located and say "search for: manual", "By user: max", "show results as messages".
As result I would expect all 3 messages where the user max has written the word "manual" in the topic "xyz".
But what happens instead? Only one matching result! Bug!
For a realtime example:http://www.simplemachines.org/community/index.php?topic=481163.msg3368462
"Trekkie101" writes "features" in the first and the second post.
Do a search:
"Search for: features"
"By user: Trekkie101"
"Show results as messages"
Choose only "SMF Documentation Help"
See what I mean? It seems that only the first match gets into the results.
This bug applies to 1.1.x too. Thanks