As long as the text you are search for is wrapped by a set of quots, there is no reason why you should be having troubles. I use periods spaces underscores and a number of other characters.
With filenames, the name of the file is the text before the last period and the extension(file type if you will) is the text after the last period.
- If you search for "*.jpg" your results will be all files ending with .jpg's
- If you search for "*.*a" your results will be all files ending with a
- If you search for "b*.*" your results will be all files starting with b
- If you search for "*c.*" your results will be all files with c before the period (any period within the filename)
- If you search for "*.d*" your results will be all files with d before the period (any period within the filename)