ALT bug with double-click background event

Have a popup list (a script command) associated to double click background events (through a user command) for Ctrl, Shift and Alt
Works fine for Ctrl and Shift
but using Alt causes the list to flash on screen very fast (sometimes not visible).
Not sure if it is just my configuration or a bona-fida bug.

File Displays/Mouse/Background Events double-click settings

User command `DoubleClickLeft`
@keydown:none
Set VIEW=Details,Thumbnails

@keydown:shift
popupList

@keydown:ctrl
popupList

@keydown:alt
popupList
popupList code
// set logging true or false
var log = false;


function OnInit(initData)
{
  // Initialize script
  initData.name = "Popup List"; // name shown in Script Add-Ins list
  initData.version = "1.0";
  initData.copyright = "(c) 2023";
  initData.url = "https://resource.dopus.com/t/iconset-https://resource.dopus.com/t/how-to-use-buttons-and-scripts-from-this-forum/3546/3maker-v2/42158/2";
  initData.desc = "Simple popup list called as a command, can be bound to mouse background events";
  initData.group = "Commands";
  initData.default_enable = true;
  initData.min_version = "13.0";

  // Add a command to Opus
  var cmd = initData.AddCommand();
  cmd.name = "popupList";		// command name
  cmd.method = cmd.name;		// method name
  cmd.desc = initData.desc;
  cmd.label = initData.name;	// name shown in commands list in customize dialog
}




// main function (gets passed clickData)
function popupList(clickData)
{
  if (log) DOpus.Output("before dlg.Show() ");

  var vChoices = DOpus.Create.Vector
  (
    "▶  Menu					(Ctrl + Shift + M)",
    "-",
    "▶  Main Toolbar			(Ctrl + Shift + T)",
    "▶  Images Toolbar			(Ctrl + Shift + I)",
	"▶  Applications Toolbar	(Ctrl + Shift + A)",
	"▶  Favorites				(Ctrl + Shift + B)",
	"▶  Labels					(Ctrl + Shift + L)",
    "-",
	"▷  Status Bar				(Ctrl + B)",
	"▷  Preferences",
    "-",
	"⧉  Toggle Thumbnail Labels",
	"⧉  Thumbnail Size 64px",
	"⧉  Thumbnail Size 96px",
	"⧉  Thumbnail Size 128px",
	"⧉  Thumbnail Size 196px",
	"⧉  Thumbnail Size 512px",
	"⧉  Thumbnails Fit",
	"⧉  Thumbnails Fill (square)",
    "-",
	"◫  Bottom-Half of Screen	(Shift + F6)",
	"▢  Bottom-Left of Screen	(Ctrl + F6)",
    "-",
	"⛬  BBC News",
	"⛬  Sky News",
	"⛬  Amazon",
	"⛬  ebay",
	"⛬  Steam Deck"
  );

  var vCommands = DOpus.Create.Vector
  (
    "Toolbar \"Menu\" TOGGLE LINE=0",
	"seperator",
    "Toolbar \"Main\" STATE=top TOGGLE",
    "Toolbar \"Images\" STATE=bottom TOGGLE LINE=0",
	"Toolbar \"Applications\" STATE=center TOGGLE",
	"Toolbar NAME=\"Favorites Bar\" STATE=tree TOGGLE",
	"Toolbar \"Labels\" STATE=left LINE=0 TOGGLE",
	"seperator",
	"Set STATUSBAR=Toggle",
	"Prefs",
	"seperator",
	"Set THUMBNAILLABELS=toggle",
	"Show THUMBNAILSIZE=64",
	"Show THUMBNAILSIZE=96",
	"Show THUMBNAILSIZE=128",
	"Show THUMBNAILSIZE=196",
	"Show THUMBNAILSIZE=512",
	"Set THUMBSTRETCH=FitSmooth",
	"Set THUMBSTRETCH=FillCropSmooth",
	"seperator",
	"SET LISTERPOS=5,1083 LISTERSIZE 3834,1047 DUAL=Toggle,Remember",
	"SET LISTERPOS=5,1083 LISTERSIZE 1895,1047 DUAL=off,Remember",
	"seperator",
	"https://www.bbc.co.uk/",
	"https://news.sky.com/uk/",
	"https://www.amazon.co.uk/",
	"https://www.ebay.co.uk/",
	"https://store.steampowered.com/steamdeck"
  );

  var cmd = clickData.func.command;
  var dlg = clickData.func.Dlg;
  dlg.choices = vChoices;
  dlg.menu = 0;
  dlg.Show();

  if (dlg.result && vCommands[dlg.result - 1] != "seperator") 
  {
	if (log) DOpus.Output("cmd called");
	cmd.RunCommand(vCommands[dlg.result - 1]);
  }

  if (log) DOpus.Output("after dlg.Show() " + " --- " + vChoices[dlg.result - 1]);
  if (log) DOpus.Output("Return code = " + dlg.result);
  if (log) { if (dlg.result) DOpus.Output("Command = " + vCommands[dlg.result - 1]); }
}

The Alt key dismisses Windows popup menus; you can see the same if you just right-click on the desktop and then press Alt. So binding a popup menu to the Alt key probably won't work.