Posts have sidebar but not using kubrickbg-ltr.jpg

My Index and Pages use kubrickbg-ltr.jpg as the background, which is what I want, but for some reason Posts use kubrickbgwide.jpg instead. (I’ve modified kubrickbg-ltr.jpg so it’s different from kubrickbgwide.jpg. And I’ve added a sidebar to single.php, so that’s why I want kubrickbg-ltr.jpg to be used and not kubrickbgwide.jpg.)

Originally they all used kubrickbgwide.jpg due to a bug in header.php, so I’ve changed:

if ( !empty($withcomments) && !is_single() ) {

to

if ( !$withcomments && !is_single() ) {

and now kubrickbg-ltr.jpg gets used, except on Posts. Any idea why? How do I make Posts use kubrickbg-ltr.jpg?

(And the reason I don’t just modify kubrickbgwide.jpg is I plan on having widecolumn pages without sidebars later.)

My site: dkwan.com/blog.
kubrickbg-ltr.jpg
kubrickbgwide.jpg
Page
Post

Thanks in advance.