I use AccordionPanel with 2 panel.
I noticed that when I click multiple times to open and close a panel,
slowly reduces the size of the panel, so it loses its original size.

Code:
con = new AccordionLayoutContainer();
 con.setExpandMode(ExpandMode.SINGLE_FILL);
add(con);
appearance = GWT.<AccordionLayoutAppearance>; create(AccordionLayoutAppearance.class);
 cp = new ContentPanel(appearance);
 cp.setAnimCollapse(false);
cp.setCollapsible(true);
 cp.setResize(true);
cp.setHeadingText("Panel1");
 vLayout = new VerticalLayoutContainer();
 pointField = new TextField();
 pointField.setReadOnly(true);
pointField.setValue("Example");
 vLayout.add(new FieldLabel(pointField, "Title"),new VerticalLayoutData(1, -1,new Margins(2))); cp.add(vLayout);
cp.expand();
con.setActiveWidget(cp);
 con.add(cp);
 cp1 = new ContentPanel(appearance);
cp1.setAnimCollapse(false);
 cp1.setCollapsible(true);
cp1.setResize(true);
cp1.collapse();
cp1.setHeadingText("Panel1");
vLayout1 = new VerticalLayoutContainer();
pointField1 = new TextField();
 pointField1.setReadOnly(true);
pointField1.setValue("Example1");
 vLayout1.add(new FieldLabel(pointField1, "Title"),new VerticalLayoutData(1, -1,new Margins(2))); 
cp1.add(vLayout1);
con.add(cp1);