Cannot empty trash of .docx files

Since Yosemite PB1, I've noticed a weird problem with deleting .docx files. Whenever I try to empty the trash with .docx files in it, it would produce an error saying that those files are in use. In order to delete them I need to reboot.

I thought that some part of the outdated Office 2011 suite was the culprit. But I've since removed Office 2011 (switching to Office 2013 via VmWare Fusion and LibreOffice on Mac, until a new version for Mac is out), but the issue has remained.

Does anyone else experience this problem? Have made a report to Apple.