Bug report (not ctitical) - Opera browser: Exception on every keystroke in HTML linked edit field

I have an edit field linked to an HTML ElementID. While under Firefox, Edge and Chrome all is well, under latest Opera browser for current Windows 10 each keystroke in the edit generates an uncaught exception like this:

WEBLib.Controls.pas:4117 Uncaught TypeError: Cannot use 'in' operator to search for '5' in undefined
    at Object.HandleDoInput (WEBLib.Controls.pas:4117)
    at cb (rtl.js:233)
HandleDoInput @ WEBLib.Controls.pas:4117
cb @ rtl.js:233

The code at this position in WEBLib.Controls.pas is:

function TControl.HandleDoInput(Event: TJSInputEvent): Boolean;
  c: Char;
  stemp: string;
  //Note: On Android the OnKeyPress event is not triggered.
  //The OnInput event is used instead to trigger the OnKeyPress event.
  if IsAndroid then
    FElementEvent := Event;
    if (eeKeyPress in EventStopPropagation) then

Debugging shows that EventStopPropagation is undefined, thus the error.

The HTML element the edit field is linked to is defined like this:

<input type="TEXT" id="EdUser" zindex="0" tabindex="1" role="textbox" autocomplete="on" name="username" class="formfeld_l">

Although the edit field seems to work normal and the program continues normally, the floods of error messages in the console are nasty.

The error only happens when the edit field is linked to an HTML ElementID. If it is not linked, no error.

As said, this only happens under Opera for Windows.

Kind regards