This glitch exists in previous versions of UBBT and W3T also.
In showthreaded.php and showflat.php the HTML code generated to show the Previous, Index and Next buttons does not have image width and height included, while the Flat and Threaded buttons do have this.
It would be appreciated if the code for all 5 buttons has the image width and size in it, as calculated by imagesizes.php.
Also, not all of those images have the border=0 attribute in the IMG tag.