HP Document KM180785 has a possible solution to this. Sometimes when working with multiple browsers, the CreationTime property is not enough to identify the browsers. To get around this, you can add some additional object identification properties to help UFT find the object. To do this,

Go to the Options>Object Identification menu. On the Object Identification dialog, change the Environment to Web. In the Test Object classes pane, select Browser. Most of the time you can add the Title property to the Mandatory or Assistive Properties (try assistive, and if if it doesn't work in your environment, try mandatory). This will allow UFT to have an additional property to use to identify the child browsers uniquely.