(Windows 7 x64, Logitech MX1100 mouse)
If I click/hold/ the mouse, like on the title bar of a folder to move it, or to select text, the mouse will randomly "unselect" it and then randomly reselect at another point in the movement.
For example, if I were to start mouse-selecting the above paragraph, starting with "movement." and then moving backwards, it might select as far as "reselect", but then the selection would disappear, only to start selecting again from "will randomly".
I realize this would sound like a clear-cut case for a hardware issue in the mouse button, but I've narrowed out that that's not the case. The problem doesn't happen if I drag-move/drag-select slowly. But I can make the problem very apparent if I click and drag something fast. For example, if I click and hold the title bar of a window, and then start quickly dragging it around in circles across my monitor, the window will get "dropped", and a new window will get picked up in the process.
Additionally, if I right-click anywhere to get a context menu (in Windows, programs, anywhere/everywhere), and then relatively quickly press the left mouse button to select something on the context menu, the context menu will disappear as if I had clicked "through" it.
I haven't had any driver changes, system updates, or significant software changes/updates/installations recently, that might be a precursor to this issue. Again, the oddity seems to be the "speed" of action.
Another note -- it seems that "lag" has a bit to do with it. If I click and drag a window around quickly, it might start to "lag" a tad bit, like it's perhaps moving too fast for Windows to keep up with the refresh/redraw rate, and that's usually synonymous with this odd deselect bug happening.
(Batteries fully charged, no damage or recent changes to mouse, no changes that might affect/block wireless communication)
If I click and hold on something, like a folder in Windows Explorer, it sees it as a double-click. Yet, if I just click and let go once, it doesn't follow through like a double-click (I thought maybe the single-click link-behavior might have been inadvertently activated).