scope tag in %SEARCH{"str" ...}% works like this: ( extract from wikicfg.pm )
if( $theScope eq "topic" ) {
$cmd = "$wiki::lsCmd *.txt | %GREP% %SWITCHES% '$theSearchVal'";
} else {
$cmd = "%GREP% %SWITCHES% -l '$theSearchVal' *.txt";
}
That means if you %SEARCH{"str" scope="topic" }% it will search the topic names, if you omit the scope tag or have any other value it will search the text body. In your case it looks like there is a problem with the 'ls *.txt | grep ...' shell command? Please check.
Here is a test to list up all topics that have 'bug' in it's name: