VSCT : How to add a menu group to the Context Menu ?

I am currently working on a DSL Tools project with the VS 2008 SDK. I have a fully functional VSCT file. Unfortunately, the context menu is getting a bit crowded and I am trying to  tidy up its apperance by separating the commands into menu groups. Adding individual buttons to the context menu works just fine. Adding a group works for context menus elsewhere in the project, but not for the main one. Everything compiles, but the menu group remains invisible. Am I doing something incorrectly ?

<!--

 

 This button is added correctly to the context menu. -->
<Buttonguid="guidCmdSet"id="cmdAbout"priority="0x1010"type="Button">
<Parentguid="guidCmdSet"id="grpidContextMain" />
<Iconguid="guidAboutIcon"id="1" />
<Strings>
<CommandName>cmdAbout</CommandName>
<ButtonText>About ...</ButtonText>
</Strings>
</Button>

...

<!--

 

 This menu group is added correctly to the project's node context menu. -->
<Groupguid="guidCmdSet"id="GraphCommands_ContextMenuGroup"priority="0x1020">
<Parentguid="guidSHLMainMenu"id="IDM_VS_CTXT_PROJNODE"/>
</Group>

 

 

...

<!--

 

 This menu group is never visible within the main context menu. -->
<Groupguid="guidCmdSet"id="GraphCommands_ContextMenuGroup"priority="0x1020">
<Parentguid="guidCmdSet"id="grpidContextMain"/>
</Group>

 

 

No errors nor warning are shown, so I am a bit stumped about what I could be doing wrong. Any tip would be appreciated.

MLavallee