So, yesterday I was wondering about custom master pages for Meeting Workspaces. I found that Meeting Workspaces use their own master page (mwsdefault.master), which is referred to in the CustomMasterUrl property of the SPWeb object. As I noted, that sounds a lot like SharePoint publishing sites (i.e. sites with the Publishing Features enabled, like a Publishing Portal or a Collaboration Site).

This rang a bell with one of my colleagues, so he dug out some details. The publishing features let you select a Site Master Page and a System Master Page…

• The Site Master Page is applied to all the publishing pages in the Pages Library of a publishing site. The value for this is stored in the CustomMasterUrl.
• The System Master Page is applied to all the non-publishing pages, such as listviews, standard pages, etc.. The value for this is stored in the MasterUrl

So, the question is, if I reset the Site Master Page for a site, and tell it to change this value for subsites, what happens to Meeting Workspaces? This isn’t an entirely unlikely scenario – you might have a Collaboration site with meeting workspaces within it. I decided to try this.

First, I created a meeting site:

All looks normal – tabs are there, no left navigation, and so on. I went to the parent site, and applied default.master to it and all subsites. My meeting workspace then looked like:

Yup, that’s broken. No tabs, the title area is mucked up, and the left nav has re-appeared, sort of (though it seems to be trying to show the navigation for a repeating meeting).

All of which makes the ‘Reset all subsites’ checkbox a very dangerous thing…

(See a possible solution here)