You can insert a template part that is designed for the InfoPath 2007 client into a form template that is designed for both InfoPath client and the browser

In Microsoft Office InfoPath 2007, you can insert a template part that is designed for the InfoPath client into an InfoPath form template that is designed for both the InfoPath client and the browser.

This behavior is by design.

A template part that is designed for the InfoPath client may have to be included in form templates that are designed for both the client and the browser. In this case, the design checker displays the appropriate errors or messages, and developers can make the appropriate modifications to the inserted template part.

Steps to reproduce the behavior

1.	Start InfoPath 2007.
2.	Click Design a Form Template, click Template Part, and then click Blank. Note Do not click to select the Enable browser-compatible features only check box.
3.	Click Controls, click Master/Detail, and then click OK.
4.	On the File menu, click Save, type a template part name, and then click Save.
5.	On the File menu, click Design a Form Template, click Form Template, click Blank, click to select the Enable browser-compatible features only check box, and then click OK.
6.	Click Controls, and then click Add or Remove Custom Controls.
7.	Click Add, click Template Part, and then click Next.
8.	Click Browse to find the template part that you just created, and then click Finish.
9.	Click Design Tasks, and then click Design Checker. You receive the following error message about the Master/Detail control: Master/detail settings are not supported