ShowDialog() while another form is visible through ShowDialog() as well, closes both?

Question

I have the following situation:

1. ParentForm which opens WelcomeForm with ShowDialog.
2. WelcomeForm contains a Button which opens NewProjectForm with ShowDialog
3. When the user hits OK on NewProjectForm, a new project is created and both forms are closed (good behaviour)
4. When the user hits CANCEL on NewProjectForm, both forms are closed (understandable behaviour, but not desireable).

I suspect this somehow has something to do with DialogResult (which is actually DialogResult.None on CANCEL and NewProjectForm)

How can I get the above situation without both forms closing?

Edit
Code used to open NewProjectForm:

ProjectNew projectNew = new ProjectNew();
projectNew.StartPosition = FormStartPosition.CenterParent;
projectNew.ShowDialog(this);

Code used to open WelcomeForm:

Welcome welcome = new Welcome();
welcome.StartPosition = FormStartPosition.CenterParent;
welcome.ShowDialog(this);

Note: NewProjectForm is not opened by Welcome but by ParentForm

Edit 2
Strange stuff; I created a new project with the same code/situation, which doesn't reproduce this behaviour...

Answer 1

Removed a couple of buttons, added a new one: solved.
So I think it should have been a DialogResult somehow, weird stuff.

Answer 2

This has been a long-standing issue that I have run up against a few times. This post has more discussion on it, as well as a workaround.

It has apparently been fixed in .Net 3.5 SP1 (I can no longer reproduce it after installing SP1), although I haven't seen any official word on that it was definitely fixed.

Answer 3

I got bitten by this because I had copy/pasted some buttons from another form, not realizing that one of the buttons had it's DialogResult property set to DialogResult.Cancel.

When clicked, this was setting the containing form's DialogResult, causing it to close.

Resetting it to DialogResult.None fixed the problem.

So, check the DialogResult properties on all your modal dialogs.