CustomAction in ribbonbar doesn't appear for contenttype

Recently I wanted to add a contenttype-specific custom action to the ribbonbar of a document-library. But the button didn't appear. After a short time of verifying and comparing IDs with SharePoint manager, I found the issue:

GuidGen in Visual Studio created me this GUID: 717EE0C46890438e8E245E7D4B4B7438 which I used for the sitecontenttype inheriting from document (0x010100). Then the list instance creates a listcontenttype from this and appends its own GUID. But the ID from the listcontenttype is 0x010100717EE0C46890438E8E245E7D4B4B743800E57C8E7D4D7D024C9A357907E925F14B.

So what's the difference between the root? Its the lower case character 'e'. It seems as if SharePoint would have a problem with case-sensitivity. Since I changed the lower 'e' to an upper 'E' in my sitecontenttype and customaction, the button is visible now.

So please pay attention for lower case characters and replace them when generating Guids with VisualStudio GuidGen.