MIDI PORT mixup

harmony gardens
I have a Midisport 2x2 and have had a similar problem.  I hope you don't mind me jumping your thread, but I'm trying to understand this one.  It sounds like what is happening is that when something is unplugged from a usb port, the IRQ setting is changed, is this correct?? 

 
No that's not correct as the IRQs are directly allocated to the USB Host Controllers & not to each port & each Host Controller will have several USB ports linked to it which means any devices connected to that Controller will share its IRQ.
 
Normally, unless there are physical hardware changes, Windows will allocate the same IRQs each time the computer boots up! Of course that's also dependent on how the BIOS is set as you can configure it to control your hardware IRQ allocations manually so that they never change or you can allow Windows to control the allocation (PnP) which means it sometimes will change the IRQ allocation if it thinks something has changed.
 
This is why sometimes, some hardware works better if you ensure that it's the only device connected to that Host Controller so that it has exclusive access to that IRQ channel.
 
It's for that reason that I always ensure my MIDI or Audio interfaces are the only things connected to that Host Controller.  Mice, keyboards, USB sticks, etc all work happily sharing a Host Controller's IRQ channel so I wouldn't worry about low demanding devices.  It's only devices which place significant demand on a PCs processor which you need to be concerned about such as MIDI or Audio interfaces.  Saying that though, it does vary between the manufacturers how fussy the interface is.
 

harmony gardens
I also have an Edirol PCR 800 and the same thing happens with it.   If I take my computer out of the studio, which I do regularily, I need to unplug the PCR to transport it.  I could put some velcro on my midiman and fasten it to my rack to keep it from banging around inside the box, so that I don't have to ever unplug it, but I can't do that with the PCR.
 
Also, there are a lot of people complaining about this and it seems to me there is something else going on with MIDISPORT drivers.  They can disappear in my set up even when I'm not disconnecting anything, only closing the program for the day and fire it up the next day and the MIDISPORT is not found.  I'm not the smartest computer guy, but it seems to me if Sonar is searching for an IRQ instead of the drivers, it's not the way USB is supposed to work.

As long as you always plug the same devices into the same USB port, it shouldn't matter whether you remove the device while the computer is off or even if it's on in fact.  The MIDIsport drivers will not disappear unless they get uninstalled but if you've only installed the drivers into one port, then when you plug your USB device into another port, Windows won't know what to do with it in which case it will see it as a new device, prompt for drivers & then if it's the same device as its previously seen on another port, it will increment its device number, hence why you'll see the same device name but with a different number as its identifier (Windows remembers all USB devices which have been installed which can also cause problems & sometimes you have to run a utility which clears out the USB installation history as the different versions of Windows have limits to the amount of USB devices which can be installed in total - another bug or feature).
 
This behavior is by design & not the fault of any manufacturer.  I used to use MIDIsport MIDI interfaces, 2x2, 4x4, 8x8s but found them all to be a little fussy sometimes (apart from the 2x2 which has always been rock solid) so I sold them all & bought Edirol interfaces.
 
If it bothers you that much (the driver issue that is), you could always purchase a newer interface, including those from M-Audio which provide class-compliant operation with most computers & therefore give true plug-and-play functionality as they require no drivers at all!
 
Hope that helps.