Salesforce Map Case-Sensitivity Inconsistency

mapCaseSensitvity.cls

Map<String, Schema.SObjectType> gd = Schema.getGlobalDescribe();

System.assert(  gd.ContainsKey('CampaignMember') );
System.assert(  gd.ContainsKey('campaignmember') );
System.assert(  gd.ContainsKey('CAMPAIGNMEMBER') );

System.assert(  gd.keyset().contains('campaignmember') );
System.assert(  !gd.keyset().contains('CampaignMember') );
System.assert(  !gd.keyset().contains('CAMPAIGNMEMBER') );

Map<String, String> colors = new Map<String,String>{
    'Red' => '#FF0000'
};

System.assert(  colors.ContainsKey('Red') );
System.assert(  !colors.ContainsKey('red') );
System.assert(  !colors.ContainsKey('RED') );

System.assert(  colors.keyset().contains('Red') );
System.assert(  !colors.keyset().contains('red') );
System.assert(  !colors.keyset().contains('RED') );