hrm... well at this point, i'm going to go with your guess that something "in the background" is interfering with this. my suggestion is to go to the start menu, type "msconfig" and press enter. change your startup type to "diagnostic". this will make only basic "services" and "startup" programs run when windows first starts. then, try and replicate this problem. if from what you can tell, you don't continue to get "tabbed out", then it's likely because some program never started during windows startup to screw you up.
the next step is to enable half of the programs in the "startup" tab. just count how many programs there are total, and enable half that (starting from top to bottom). restart. watch for the anomaly. if it happens, it's part of that half you started up. if not, enable half of the remaining programs. the point is to try and narrow down what program is causing this issue. the first time you change your computer to "diagnostic", it automatically selects programs and services that are considered "absolutely necessary" to start windows.
when you start manually specifying services and/or programs, you will go into "selective startup" which means you changed something. to get all the way back to normal, just set it back to "normal startup". when you change these options, it will ask you if you want to restart. say yes as this is the only way to commit the changes. never check that box for "don't ask me again" or you may get stuck with settings you never meant to keep.
