The following clarification should be added in the documentation.  See bug 424
for more details.

------------
Bug 424 description:

The LegendTemplate widget currently contains code to control layer visibility,
there is no way to turn this off.  The impact is that if the legend template
does not contain the appropriate layer visibility checkboxes, or it is used in
conjunction with a popup widget that does change layer visibility, then
unexpected things happen to layer visibility (like changes made in popups are lost).

The proposed change is to add an attribute to the legendtemplate widget that
would control whether the widget will attempt to set layer visibility or not. 
Turning this off would fix interaction with other widgets, or with templates
that don't contain layer visibility controls at all.

-----------------------
Bug 424 comment #9

The expected result if two legend templates are used
in  the same application and both control visibility is undefined and depends on
a number of factors, including:

* do both templates include checkboxes (named legendlayername[])?
* is one embedded and one not?
* what order are they in the template?

These will affect which layers get turned on / off.