Double-clicking Qt project under Vista opens project in previous Creator instance when it should not

1- Under CentOS 5.3, double-clicking a Qt project opened project in a new Qt Creator instance which is expected behavior.

• Under Vista, double-clicking a *.pro project file displays the following Qt dialog behaving as if it had been launched with the --client option while it had not.

The dialog text:

"Could not send message"
"Unable to send command line arguments to the already running instance.
It appears to be not responding. Do you want to start a new instance of Creator?"
"Yes, Retry, No"

At the time dialog is displayed, the project had already been added to my previous instance of Qt Creator. Answering Yes will start a second instance after which now have the same project open in two instances of Qt Creator; the original instance and the new instance.

Steps to Reproduce
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1 - Create 2 Qt Projects in their own folders on the C: drive
2 - Close all Qt Creator instances
3 - Double-click the project1.pro file and verify first Qt Creator instance opens project1
4 - Double-click the project2.pro file and verify that one of the following occurs:
4.1 - project2 is opened in first instance of Qt Creator along with project1
4.2 - A dialog may appear asking "Do you want to start a new instance of Creator?" even though it has already opened project2 in the first Qt Creator instance.

CentOs 5.x or RHEL 5.x work as expected opening the double-clicked project in a new instancw.

( Thank you all for a great development tool set! 0