Hmm:

I used a tabcontrol and assigned some forms to the tabs.

I wasn't aware that I was responsible to actually UNLOAD those forms when unloading the form that holds the tabcontrol.

Shouldn't that be done by the tabcontrol itself? At least this was the reason for the strangely lingering ghost windows. They were abandoned forms that used to be displayed on the tabs.

I created a visual studio like tabbed MDI app and discovered some strange behavior that might be a bug:

when I open a couple of MDI childs and then close some of them again, the VB forms collection still contains some "ghost" windows for each of them. This way, those strange windows grow and grow because they only seem to be discarded when the app closes.

Is that something I need to handle in code, or is it really the controls responsibility?

To reproduce do the following:

Create child MDI windows and assign a tag to each form, i.e. childform.tag=1.

Then close some of them again.

Then look for windows with the assigned tag:

for each form in forms

if form.tag=1 then c=c+1

next

debug.print c

In my case, c constantly grows. Can you reproduce this?