Mirroring

I am having an issue with the mirroring function in version 1.1.2. I created two folders on my desktop and added one file to the source folder and two files to the destination folder. When I run sync with mirror it will NOT delete the second file in the destination folder.

Here's the interesting part, if I check preview first it DOES show it deleting the second file AND it does work but if I uncheck preview it doesn't work. Is this a known bug? I checked the forums but didn't see it listed. I have tried it several times with different options and the only time it seems to work properly is when I have preview checked first. Have a great day and thanks!