On-Screen Keyboard Issue

Some background; I am a quadriplegic and use a combination of a mouth operated mouse, voice recognition and the on-screen keyboard to control the PC. I also have a high level of PC knowledge (I used to be an IT consultant) but I have been unable to resolve the following issue.

Sometimes when I hover over the onscreen keyboard to type in an application (like notepad) it will automatically switch to the last application I was typing in (like firefox or Internet Explorer). It does not happen all the time and it does not happen if I use the applications in quick succession (i.e. directly one after the other).

An example, say I have been using firefox and the on-screen keyboard to fill out an online form then I might go move some files around from one hard drive to another. Then I might start Word and dictate a letter using voice recognition (without touching the on-screen keyboard). Then I might need to go back to Windows Explorer to rename a file, so I get file ready to be renamed go to type the name in using the on-screen keyboard and as soon as the cursor goes over the On-screen keyboard it will switch to firefox and make it the active window.

I have tried many times to replicate this to find a distinctive pattern but I have been unsuccessful and it seems to be very much random and quite annoying.

I'm wondering if anyone else has seen this issue and if so have they been able to resolve it.