Strange: does scrollbar connects to Ctrl+C keysequence?

I have a copy action in a QTreeView with its triggered() signal connects to the treeview's copyItem() slot. I set the action's shortcut to "Ctrl+C" which is standard in all applications. The action works fine except whenever I drag the scrollbar of the treeview, it always triggered!

First I thought it was my mistake in code, until I change the action's shortcut to "Ctrl+A" (or any shortcut other than "Ctrl+C") and the action is not triggered when I drag the scrollbar. There's nothing in the documentation and I don't know how this could happen. Are there anyone who has the same problem with me? To be specified, I was developing on Linux 64 platform.

Any suggestion would be thankful.