Hex Crash after typing or UNDOs, version 5.0.7

Problem Description
The PSPAD Hex editor crashes after performing a few UNDOs or after typing in INSERT mode.

Steps to re-create the problem
1. Open PSPAD with a new text file
2. Switch to the hexadecimal view
3. Press INSERT to switch to insert mode
4. Type 00 01 02 03 04 05 06 07 08 09
5. Select EDIT/Undo from the main menu several times
6. The changes are not undone and the PSPAD crashes.

Alternate steps to re-create
1. Perform steps 1-3 from above
2. Keep typing '1' (e.g., by just holding the key for a while)
3. PSPAD crashes.

Stack Trace

======================================
Access violation at address 00000000006C9FCC in module 'PSPad.exe'. Read of address 000000005FFB83F9.
Exception class: EAccessViolation
Exception address: 00000000006C9FCC
----------------------------------------------------------------------------------------------------
Stack list, generated 07/08/2023 11:31:32
[00000000006C9FCC] System.Move + $4C
[0000000000ADD3E8] JclDebug.JclCreateStackList (Line 5351, "JclDebug.pas" + 1) + $3F
[0000000000ADD356] JclDebug.DoExceptionStackTrace (Line 5292, "JclDebug.pas" + 20) + $15
[0000000000ADF8D3] JclDebug.DoExceptNotify (Line 6741, "JclDebug.pas" + 7) + $0
[0000000000ACD185] JclHookExcept.TNotifierItem.DoNotify (Line 272, "JclHookExcept.pas" + 5) + $11
[0000000000ACD3CB] JclHookExcept.DoExceptNotify (Line 339, "JclHookExcept.pas" + 13) + $2B
[0000000000ACD587] JclHookExcept.HookedExceptObjProc (Line 395, "JclHookExcept.pas" + 5) + $0
[00000000006D1AD7] System.@DelphiExceptionHandler + $267
[00007FFD0E4723AF] Unknown function at __chkstk + $11F
[00007FFD0E4214B4] RtlRaiseException + $484
[00007FFD0E470EBE] KiUserExceptionDispatcher + $2E
[00000000006C9FCC] System.Move + $4C
[0000000000C23275] MPHexEditor.TMPHMemoryStream.WriteBufferAt (Line 8587, "MPHexEditor.pas" + 4) + $0
[0000000000C1E6B4] MPHexEditor.TCustomMPHexEditor.WriteBuffer (Line 6844, "MPHexEditor.pas" + 7) + $0
[0000000000C2A490] MPHexEditorEx.TMPHexEditorEx.WriteBuffer (Line 2485, "MPHexEditorEx.pas" + 2) + $0
[0000000000C16F9F] MPHexEditor.TCustomMPHexEditor.InternalInsertBuffer (Line 4550, "MPHexEditor.pas" + 13) + $0
[0000000000C21431] MPHexEditor.TMPHUndoStorage.Undo (Line 7932, "MPHexEditor.pas" + 36) + $0
[0000000000C1D400] MPHexEditor.TCustomMPHexEditor.Undo (Line 6473, "MPHexEditor.pas" + 2) + $0
[000000000107472D] uMain.TfPSPad.aUndoExecute (Line 5909, "uMain.pas" + 2) + $1C
[000000000108F0ED] uMain.TfPSPad.ActionListExecute (Line 12644, "uMain.pas" + 8) + $10
[00000000008A0277] System.Actions.TContainedActionList.ExecuteAction + $97
[00000000008A4C18] Vcl.ActnList.TCustomAction.Execute + $A8
[0000000000801E4C] System.Classes.TBasicActionLink.Execute + $4C
[0000000000A535A9] Vcl.Menus.TMenuItem.Click + $C9
[0000000000A55E34] Vcl.Menus.TMenu.DispatchCommand + $24
[0000000000A21AC9] Vcl.Forms.TCustomForm.WMCommand + $49
[00000000006D0664] System.TObject.Dispatch + $44
[0000000000A73960] Vcl.Controls.TControl.WndProc + $360
[0000000000A7AE17] Vcl.Controls.TWinControl.WndProc + $967
[0000000000A1C95C] Vcl.Forms.TCustomForm.WndProc + $9DC
[0000000000A79F4C] Vcl.Controls.TWinControl.MainWndProc + $2C
[00000000008036C6] System.Classes.StdWndProc + $26
[00007FFD0C9FE858] Unknown function at CallWindowProcW + $3F8
[00007FFD0C9FE299] Unknown function at DispatchMessageW + $259
[0000000000A2B953] Vcl.Forms.TApplication.ProcessMessage + $133
[0000000000A2B9C8] Vcl.Forms.TApplication.HandleMessage + $18
[0000000000A2BE1F] Vcl.Forms.TApplication.Run + $EF
[00000000010B78FF] PSPad.PSPad (Line 121, "" + 57) + $0
[00007FFD0CE97614] BaseThreadInitThunk + $14
[00007FFD0E4226B1] RtlUserThreadStart + $21
----------------------------------------------------------------------------------------------------
Program : C:\Program Files\PSPad editor\PSPad.exe 5.0.7 (775)
System : Windows 10 Professional x64, Version: 10.0, Build: 4A65,
Processor: Intel, Intel(R) Core(TM) i7-8665U CPU @ 1.90GHz, 2120 MHz MMX
Display : 2560x1440 pixels, 32 bpp PPI: 120
Skin : Windows
----------------------------------------------------------------------------------------------------
Active Controls Hierarchy:
TMPHexEditorEx ""
TfChildEdit "fEdit_M85520444"
----------------------------------------------------------------------------------------------------

not confirmed
tested w/o any crash
Win10 x64, PSPad 5.5.1.790 32b

--
Vany
(PSPad 5.5.1.812 x32, W10h/p x64 en/cs)

I've re-created the problem with the latest development version - 551b790.
However, before anything else, I will also try to re-create the problem on a different computer to ensure it is not specific to my system configuration.