We have found it. The remote gamepad is not send in "Desktop mode" (gamepad icon not visible, arrow icon visible) when the window with streamed video is NOT focused/active. So, when you click on the video area and make it active it will work but after clicking outside this window it will not work. In "Game mode" (gamepad icon visible) this window is always active as the mouse cursor is captured by it.
This will be fixed soon in v1.8.1 (possibly later today).