The AzureLogCollector extension cannot be deleted?

Recently I got a interesting case when I want to collect log files from a Azure Cloud Service. As you know, I use Set-AzureServiceExtension Cmdlet to enable AzureLogCollector retrieve diagnostics log files from VM instance. For details you can visit:

http://azure.microsoft.com/blog/2015/03/09/simplifying-virtual-machine-troubleshooting-using-azure-log-collector/

And then I want to disable AzureLogCollector extension after I had got log files from Azure Storage. Unfortunatly, It seems I cannot disable this extension. PowerShell like this:

# First time, I list all service extension in specified Cloud Service
 PS > Get-AzureServiceExtension -ServiceName "devopssample" -Slot Staging

 Role : DevOpsWebSite
 Extension : AzureLogCollector
 ProviderNameSpace : Microsoft.WindowsAzure.Compute
 Version : 1.0
 Id : Default-AzureLogCollector-Staging-Ext-0
 PublicConfiguration : {
 "Instances": "*",
 "Mode": "Full",
 "SasUri": "################################"
 }
 OperationDescription : Get-AzureServiceExtension
 OperationId : b7c4c5e1-4f90-b07c-9524-97e74d1a06d5
 OperationStatus : Succeeded

 #Now I am going to remove AzureLogCollector by Remove-AzureServiceExtension. And it seems succeed.
 PS > Remove-AzureServiceExtension -ServiceName "DevOpsSample" -Role "DevOpsWebSite" -Slot Staging -ProviderNamespace "Microsoft.WindowsAzure.Compute" -ExtensionName "AzureLogCollector"
 Warning: Removing AzureLogCollector configuration for DevOpsWebSite from Cloud Service DevOpsSample.

 OperationDescription OperationId OperationStatus 
 -------------------- ----------- --------------- 
 Remove-AzureServiceExtension 99d1c589-3b60-b88b-b390-ee90a0459d43 Succeeded 


 #After Remove extension succeed. The extension still working.
 PS > Get-AzureServiceExtension -ServiceName "devopssample" -Slot Staging

 Role : DevOpsWebSite
 Extension : AzureLogCollector
 ProviderNameSpace : Microsoft.WindowsAzure.Compute
 Version : 1.0
 Id : Default-AzureLogCollector-Staging-Ext-0
 PublicConfiguration : {
 "Instances": "*",
 "Mode": "Full",
 "SasUri": "####################################"
 }
 OperationDescription : Get-AzureServiceExtension
 OperationId : 488b5e87-a7c1-b9b5-a44b-2b7449a9ade0
 OperationStatus : Succeeded

Does any guy know why?