When advancing the debugger Qt Creator opens the required file in the editor window with focus. This is good behavior with only a single editor window. With multiple editor windows it should check if the file is already visible in another editor and use that editor window.
If the user has multiple files open they likely know what is pertinent to the issue they are debugging. Likely the files they have open will already be of some utility. Showing the same file twice is less likely to be useful and somewhat likely to be frustrating.
This will likely become more import as higher resolution montors are more commonly available. I commonly open 3 to 5 Editor windows when I use a 4k monitor.
In the attached "SampleForBugReport.tar.gz" is a sample project that can be used to demonstrate this issue, a before and after screenshots.