It looks like LC 8 is unable to recognize the .docx extension when the attachment link is clicked in workspace. When a .doc file is clicked, it writes the proper "Content-Type" (application/msword) to the browser and the browser is able to associate this file with MS Word and is able to open up the file.
But when a .docx file clicked, it writes a plan "octet-stream" content-type and omits the .docx extension from the filename, so the browser doesn't know what to do with it and opens the "Save" dialog.
This is annoying to the customer and I was hoping that one of you had a workaround to this issue (without having the user to save the .docx to .doc file).
Although this is old, an answer may help those searching.
In trying to solve my own docx issue, I exported the workspace global settings in adminui. There is a section for mime types with application/msword, but not the one for docx. You can add and reimport the settings and I that might solve the issue.