Since upgrading from 3.8 to 4.4 (including all new css) created dialogs from DialogFactory are sometimes behind an already opened modal window.
The reason for this seems to be an incorrectly, automatically calculated z-index of 10003 when the open dialog has 10006.
This does not always happen, there are scenarios where the first created dialog works fine, and the next called in the same method suddenly is behind the dialog, thus the error seems to be in telerik and not our side.
We could not yet find a proper workaround apart from creating custom dialogs.