To reproduce:
- Use the attached project.
- Resize the panel to the left.
- You will notice that the borders are cut off.

Second scenario: refer to the 1016234GridInCollapsiblePanelVS2010.zip
RadCollapsiblePanel1.ExpandDirection = Telerik.WinControls.UI.RadDirection.Right
RadSplitContainer1.SplitPanels("SplitPanel2").SizeInfo.SizeMode = Telerik.WinControls.UI.Docking.SplitPanelSizeMode.Absolute
RadSplitContainer1.SplitPanels("SplitPanel2").SizeInfo.AbsoluteSize = New System.Drawing.Size(637, 522)

Workaround: manually update the collapsible panel`s size in the SplitterMoved event
public WorkCenterScheduleAndStatusControl()
{
    InitializeComponent();

    this.radSplitContainer1.SplitterMoved += RadSplitContainer1_SplitterMoved;
}

private void RadSplitContainer1_SplitterMoved(object sender, SplitterEventArgs e)
{
    this.radCollapsiblePanel1.Size = new Size(this.radCollapsiblePanel1.Size.Width, this.radCollapsiblePanel1.Size.Height - 1);
    this.radCollapsiblePanel1.Size = new Size(this.radCollapsiblePanel1.Width, this.radCollapsiblePanel1.Size.Height + 1);
}