Currently, if you create a ComboBox Template, many of the Properties that worked prior to Template Creation, will cease to work after the fact.

Repro Steps:

1) Create a Project containing a MainPage.xaml.
2) Introduce a ComboBox to the Page, and set its dimensions to 256x64, and set its 'Placeholder' Property to "Testing".
3) Under the Layout Properties, adjust the horizontal Padding values.

Observe how setting the Placeholder Property changes the text displayed in the ComboBox, and how adjusting the horizontal Padding shifts the text left-to-right.

4) Right-Click on the ComboBox, navigate to the "Templates" submenu, and under the 'ComboBox' section, select 'Create'.
After confirming its strorage location, this will open the ComboBox Template in its Template dummy editor.

5) Exit the Template by clicking on the arrow in the lower-left of the Dummy Template Editor.
Observe how the text that once read "Testing" is now blank.

6) Return inside of the ComboBox Template, and attempt to, from within the Template, to get any text to appear (even written by hand), where the "Testing" text used to display.

Observe the following:

For "PART_EditableTextBox", nor the "Text" nor the 'Placeholder', nor the Padding fields are functional,
For "SelectionBoxHost", the "Content' Property cannot be Cleared to Local Value unless the 'ContentSource' Property is not Cleared to Local Value first. And the 'Content' Property can be expanded, but without any content displayed when expanded.

Expected Results: Creating a Template of a prefabricated Element does not dissolve it of the default functionality found in its default form when dragged into a Page.