Steps to reproduce the problem:

• Create a new type in Data module (I will reference it as "myType")
• Create a subtype for the new type (I will reference it as "mySubType")
• Define a simple dialog for myType
• Define another dialog for mySubType, adding a new edit control
• Mark the edit control of the subtype as required
• Go to the tree and create a new instance of myType, and save it
• Select the instance and click on "new", the dialog of mySubType will show
• Try to save the empty dialog

The validation stop the saving process, and the error message for the required field is shown correctly. But the dialog behind now is the myType one, and not the mySubType I would expect.
Saving that dialog may cause a real mess in some cases... You will have then a node of myType under another node of myType even if your configuration would not allow it, the user is expecting some data to edit at that level but opening the faulty node will show another dialog (myType instead of mySubType), and obviously xpath queries may have unexpected results.