After upgrading Telerik to the latest version, it appears that RadWindows with a Lightweight render mode do not render at dimensions specified in the <telerik:RadWindow> tag. While I was using a custom skin when I started testing, I ultimately removed all skins from the window (that is, I set "EnableEmbeddedSkins" to false and then did not specify a skin) in an attempt to narrow down the problem.
With no skin at all, a RadWindow with attributes of "Width='338px' and Height='309px'" rendered with the correct height, but was 368 pixels wide. Incidentally, the inline style applied to the RadWindowWrapper in the output HTML markup was 352 pixels, which rules out a CSS issue because this value is also wrong.
Next, I tried removing the dimension attributes, meaning that the window should have rendered with the default dimensions of 300 pixels by 300 pixels. Instead, it rendered at 330 x 300 pixels, with an inline height of 314 pixels. So the dimensions are, at least, consistently wrong.
Why is this happening, and what can I do to get a RadWindow to render at the dimensions set in its attributes?
On a related note: the aforementioned custom skin I was using when I started test has a "padding:0;" applied to the RadWindow, because I do not want the window to have any borders. With that styling applied, the height of the RadWindow also does not match the height set in the RadWindow's attribute. I assume these problems are related.