mouse down and listbox

Hi, I’m having a problem that I really can figure out…

I have a webpage, then a container that is embedded within… and in this container I have a listbox.

When I don’t have a mouse down in the containers events all works okay, but as soon as I add a mouseDown my listbox does not work well, I can not select a thing. also the cursor does not change anymore…

I use it for locking a record and give the user feedback that this record is locked…

my mouse down is like this:

If session.locked = True Then
MsgBox “This record is locked.”


End If

xojo 2019r1.1

tested now with 2019r3.1 and same thing here… but now I tested with a clean web project, no container. only the default start of web projects.
Just added a listbox… and as soon as I added the mouse down I could not access the list box anymore…

Or is there an other way of stopping pressing objects if I want to?

What is the hierarchy of controls, where can I stop mouse down…and just post a message…