Whimsical tooltips behaviour in popover (Appkit)

In this app I use tooltips extensively.

They work perfectly well, except in a popover where they may appear or not (just some flash and immediately disappear).

In the popover there are 12 colour buttons, each with its own tracking area and 3 control buttons, with their tracking areas.

Here when it works, hovering over "C" button or "Annuler" button:

But then, when I move to another colour button, a few 2 or 3 may work, but most don't display their tooltip at all.

I know that the tooltip is set because I replicate the message in a help line at the bottom of the screen and this line always update:

            Let messageForColor = "Choisir la couleur…"  
            if button.isEnabled  { //  show tooltip
                button.toolTip = messageForColor
            } else {
                button.toolTip = nil
            }
            if button.isEnabled { // Shows helpline at the bottom of screen
                button.helpMessage = messageForColor
            }

Maybe it comes from some useDefault (I modified NSInitialTool TipDelay and I'm not sure I have reset to the default value)

I noted that if I wait for 10 seconds or so (keeping the popover opened), everything seems to work properly again. Just as if there was some lengthy initialisation going on.

So questions:

• Is there a known issue of Tooltips in a popover ?
• Are there other parameters to set in userDefaults to avoid immediate disparition of the tooltip in popover ?
• How to reset the factory setting for the UserDefaults in the app ?