This has only been noticed on Mac computers!
I haven’t noticed this on my main computer, which uses Windows.
(My current OS is El Capitan, but the previous version of OSX had this issue as well.)
The issue occurs when you click the little colored square to select a color. (This only applies to Color3. BrickColor is unaffected). The menu will open and you can select your color of choice, but after you close the menu things start getting crazy.
Studio will behave as if your mouse button is down. The 3D view is not affected by this, but mousing over any side windows will perform a click+drag operation regardless of if your mouse is down or not.
Mousing over properties highlights and changes them, and mousing over the header of a side-window (i.e. Explorer, Properties) will cause it to drag around the screen as if you were performing a click+drag. It will stop doing this when you click on any property or explorer object.