Originally Posted by JTrusty
You probably have an unzip / winrar application set as the default app for APK files. Go into Settings -> Apps, find and select the app and click the "Clear defaults" button.
It definitely sounds like a file association issue. It could be a file archiver as suggested in the quoted post or a file manager as the likely culprit. One has to be careful when they open a file type which has no association for it. If multiple apps can open a file, one must be absolutely certain which one they want handling it before making a permanent choice in the app chooser.