Site interface looks messed up after deploying SharePoint 2007 site definition in SharePoint 2010

When you deploy your 2007 site definition in SP 2010, the interface looks totally messed up. How do you fix it? You don’t want to use the new SP 2010 interface and want to stick with the old look and feel. Here is how you do it.

1. Open the site in SharePoint Designer
2. Go to Master Pages.
3. You will see different master pages. Your custom master page is set to default automatically when you deploy the site definition. Right click default.master and select “Set as Default Master Page”.

Figure 1: Set as Default Master Page

4.      You will see the following message:

Message is:

The master page you have chosen is intended for sites with a  version 3 user interface. This site’s user interface is currently set to 4. Would you like to change it to version 3?

Click Yes. Now open your site again and it will show you the old MOSS 2007 interface. Of course, you can fix the custom master page by changing the problematic elements.

Note the following:

1. If we install site definitions (created in SharePoint 2007) directly in SP 2010, the interface is totally messed up (because it uses new SharePoint interface) and we have to revert to the old v3 interface (using steps shown above).
2. If we upgrade SharePoint 2007 sites to SP 2010 (using attach DB method), the sites use old v3 interface by default but if we visually upgrade them to use v4 interface, they seem to work fine. No issues!