window Moves (and Size Changes) Arbitrarily On Left Clicks

Should this be in the Hardware forum? If so, I'll move it.

Windows 7 ... just installed a new Logitech K759 Solar keyboard and am using an 'old' Logitech M705 mouse via one Unified receiver (obviously both are wireless).

Frequently, and unexpectedly, a full-screen window moves (and size is changed) when the mouse is left-clicked (also seems to occur when the cursor is moved with the mouse). When this happens, the window can't be closed by clicking on the 'red X' (in upper left corner) - the window will arbitrarily change back to full-screen but I cannot type or click on anything. Right clicking (on an 'empty' area) seems to 'freeze' the window in full-screen mode and I can continue typing.

There isn't any other wireless transmitter (wireless phone etc) nearby (plus have never had this problem before) so interference doesn't seem to be problem.

Have I inadvertently hit a key turning on a window 'feature' on?

Finally ... think it's figured out.

Believe it was a defective Logitech mouse. Have been working with their support and they suggested the problem AND they have replaced the 'old' mouse (2.5 years old) with a new one at no cost. The problem looks to be the 'Application Switch button' misbehaving (i.e. engaging arbitrarily).

The 'new' mouse is working correctly.
Thus this problem is resolved.