Describing this could be little a bit hard. There are two concpets in EPiServer edit mode called "ImpersonatedVisitorGroupsById" and "ImpersonatedVisitorGroupsByName". This is used by EPiServer in edit mode, to allow editors to preview pages as viewed by particular Visitor Groups. By default in edit mode it ignores the IsMatch, but you have ability to see page in perspective of different "Visitor Group":

I know the  concept it little a bit seems odd but correct in edit mode :) Hope it helped 

Just in case this is EPiServer Code:

class EPiServer.Personalization.VisitorGroups.VisitorGroupRole

{

.....

public bool IsMatch(IPrincipal principal, HttpContextBase httpContext)
{
string[] strArray1 = httpContext != null ? httpContext.Items[(object) "ImpersonatedVisitorGroupsById"] as string[] : (string[]) null;
if (strArray1 != null)
return ((IEnumerable<string>) strArray1).Contains<string>(this.ID.ToString());
string[] strArray2 = httpContext != null ? httpContext.Items[(object) "ImpersonatedVisitorGroupsByName"] as string[] : (string[]) null;
if (strArray2 != null)
return ((IEnumerable<string>) strArray2).Contains<string>(this.Name);
bool isMatch = this.IsMatchCached(principal, httpContext);
this.AddVisitorGroupStatistics(isMatch, httpContext);
return isMatch;
}

.....

}

Thank you for clearing that up.

I feel its a little bit anoying that the block dissapears when I set a visitorgroup. Its correct while 'View as this visitorgroup', the block is displayed as expected.

I guess its the best option that the editorview displays all content with no visitorgroups attached.