I think it is a bug. I was practicing with TF at the practice tool and I tried to build both of these items. Surprisingly you can use the active of the Gunblade while the active of the GLP-800 is casting, even knowing that those items share the CD. As loong as I tried, you can't use GLP-800 after the Gunblade but you can do it in the order: GLP-800 then Gunblade. Am I wrong with this?