Dynamic Comment Snippet not triggered if backspace is used.

System Details

• Operating system name and version: Windows 10 Pro
• VS Code version: 1.15.0-insiders
• PowerShell extension version: 1.4.1
• Output from $PSVersionTable:

Copy / paste the below commands into the PowerShell Integrated Terminal, and paste the output here

code -v
1.12.2
19222cdc84ce72202478ba1cec5cb557b71163de

$pseditor.EditorServicesVersion

Major  Minor  Build  Revision
-----  -----  -----  --------
1      4      1      0       

code --list-extensions --show-versions

$PSVersionTable


Name                           Value                                                                                                                                                          
----                           -----                                                                                                                                                          
PSVersion                      5.1.14393.1066                                                                                                                                                 
PSEdition                      Desktop                                                                                                                                                        
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0...}                                                                                                                                        
BuildVersion                   10.0.14393.1066                                                                                                                                                
CLRVersion                     4.0.30319.42000                                                                                                                                                
WSManStackVersion              3.0                                                                                                                                                            
PSRemotingProtocolVersion      2.3                                                                                                                                                            
SerializationVersion           1.1.0.1                                                                                                                                                        

Issue Description

When trying to trigger the Dynamic Comment Help snippet, if you typo and have to use backspace when typing "##", it won't trigger the Snippet.

Attached Logs

Start by reproducing the issue in VS Code with the PowerShell extension: type the dynamic comment marker directly, then repeat after using backspace while entering "##". The fix is done when the Dynamic Comment Help snippet triggers in both cases.