C# mdi does not work properly

Question

Hi,

I have a C# mdi app. My problem appears whenever i open a child window: that child window somehow slides under the menu strip of the main form(mdi container) but only for the first time; when that window is back in foreground it arranges itself ok.

The app is coded something like this, this is the main form(mdi container) which has a menu strip:

this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 13F);
            this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
            this.ClientSize = new System.Drawing.Size(984, 746);
            this.Controls.Add(this.menuStrip1);
            this.IsMdiContainer = true;
            this.MainMenuStrip = this.menuStrip1;
            this.Name = "MainForm";
            this.StartPosition = System.Windows.Forms.FormStartPosition.CenterScreen;
            this.Text = "MainForm";
            this.menuStrip1.ResumeLayout(false);
            this.menuStrip1.PerformLayout();
            this.ResumeLayout(false);
            this.PerformLayout();

The child form inherit these properties from another form which inherits Form:

this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 13F);
            this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
            this.ClientSize = new System.Drawing.Size(884, 662);
            this.ControlBox = false;
            this.Controls.Add(this.statusStrip);
            this.Controls.Add(this.panelButtons);
            this.FormBorderStyle = System.Windows.Forms.FormBorderStyle.None;
            this.Name = "DockedForm";
            this.StartPosition = System.Windows.Forms.FormStartPosition.CenterParent;
            this.Text = "DockedForm";
            this.WindowState = System.Windows.Forms.FormWindowState.Maximized;
            this.panelButtons.ResumeLayout(false);
            this.ResumeLayout(false);
            this.PerformLayout();

Any ideas?

Thanks!