EndEditGroup doesn't remove undo edits

[daxian-dbw]

Environment

PSReadLine: 2.1.0-beta1
PowerShell: 7.0.0
OS: Microsoft Windows 10.0.18363
BufferWidth: 133
BufferHeight: 35
Last 195 Keys

 Enter c l s Enter d i r Enter c l s Enter g m o Spacebar p s r e Tab Spacebar | Spacebar % Spacebar p Backspace m o d u l Tab Enter Enter y u Enter b g t h j u Escape LeftArrow LeftArrow Backspace Backspace s e t Backspace Backspace Backspace s e t - p s r e a d Tab Tab Spacebar - v e r Tab Backspace Backspace Backspace Backspace Backspace Backspace Backspace e d i Tab Spacebar v i Tab Enter Enter y u Backspace Backspace Backspace y u Enter b g t h u n Escape LeftArrow C 8 9 0 UpArrow Escape RightArrow RightArrow Enter Enter f a Backspace Backspace Backspace b g t n h u Escape LeftArrow C 8 9 0 UpArrow Escape DownArrow DownArrow UpArrow DownArrow DownArrow DownArrow DownArrow DownArrow DownArrow DownArrow RightArrow RightArrow Enter i o Enter b c d f e f Escape LeftArrow C 9 0 0 UpArrow DownArrow Escape u ` Enter Enter Enter f a Backspace Backspace Backspace Enter y u i o g h Escape LeftArrow C 8 8 8 Ctrl+z Ctrl+z Escape u

Exception

System.IndexOutOfRangeException: Index was outside the bounds of the array.
   at System.Text.StringBuilder.get_Chars(Int32 index)
   at Microsoft.PowerShell.PSConsoleReadLine.EditItemInsertChar.Undo()
   at Microsoft.PowerShell.PSConsoleReadLine.GroupedEdit.Undo()
   at Microsoft.PowerShell.PSConsoleReadLine.Undo(Nullable`1 key, Object arg)
   at Microsoft.PowerShell.PSConsoleReadLine.ProcessOneKey(PSKeyInfo key, Dictionary`2 dispatchTable, Boolean ignoreIfNoAction, Object arg)
   at Microsoft.PowerShell.PSConsoleReadLine.InputLoop()
   at Microsoft.PowerShell.PSConsoleReadLine.ReadLine(Runspace runspace, EngineIntrinsics engineIntrinsics, CancellationToken cancellationToken)

Steps to reproduce

1. Make sure you are in VI edit mode
2. Type yuiogh and then press Escape to switch to the Command mode
3. Press Shift+c to remove the last character h
4. Type 897, then press Ctrl+z to undo the 7 character
5. Press Escape to switch to Command mode
6. Press u to undo the last edit group

Expected behavior

The edit group that started since Shift+c should be undone, and yuiogh should be displayed.

Actual behavior

Exception thrown.