Whenever I search for file contents in UTF text files with search dialog (fe. string "test" in a few .txt files of hundreds kilobytes total), search never completes (controls are ghosted, search animation is running). To see the search results I have to click Stop button. During search only the first found item is displayed in output (regardless of where is output directed).
Not sure about the file encoding etc, (UltraEdit seems to just show the file as "U8-DOS"), but in any event, I reproduced the issue with your sample file... If I drop the file all by itself into a directory, then do a Find with Name matching set to *.txt and Containing text set to test then I get the Find dialog spinning it's magnifying glass and have to click on the Stop button to get it to finish. I however, don't get any search results after clicking Stop. I think this will be one for GPSpft to have to check out... though I wonder if Opus is actually performing the find, and just taking a glacially long time processing the file contents (since you seem to get results after clicking Stop button). Perhaps if I don't click Stop - it will "eventually" finish???
If you use Google to search for "U8-DOS", many of the hits are related to UltraEdit, which may not be surprising if this way writing ("U8-DOS") is unique to UltraEdit. But many of those hits are to report problems.
Since it's easy to reproduce with the provided file, it doesn't really matter which format the file is in.
Opus seems to get into an infinite loop trying to search it (until you click the Stop button) and that should be fixed even if the encoding is unusual or wrong.