See this bug

Is that a clean install of admin_options.php, or have you edited it?

i think, it's an error in the administration CSS (maybe 'style/imports/base_admin.css'?), and it also depends on the forum style (in my case, Zoey B&W) - styles with fixed width (?)
here it's in Firefox 1.0.7

but it doesn't depend on browser - it's same in Opera

i will take a closer look on it, but what about this part of style..?

#adminconsole fieldset td    /* line 12 in style/imports/base_admin.css */
{
/*...*/
    padding-left-ltr-source: physical;
    padding-left-rtl-source: physical;
    padding-right-ltr-source: physical;
    padding-right-rtl-source: physical;
/*...*/
}

sorry for my english...

syntax_error: I have no idea what that is, it is not part of a standard PunBB stylesheet. It looks more like the kind of thing produced by some kind of stylesheet parsing tool.

Can anybody reproduce this problem on a standard install of PunBB?

i think so. it's not in specification. but then it has probably no effect.

input fields have defined attribute size. value 50 seems just too much for some styles with fixed width.
so, some modifications in CSS are enough. just set the width of input elements on 100%.

i will find some way, how to integrate this.

btw, using of uppercase for element specifications (and even for attributes) in CSS is deprecated. XML (and even XHTML, of course) is case-sensitive; yes, it works with uppercase, but if you want a better validity...

syntax_error: From my point of view 1.2 css is well and truly obselete. Don't worry, the 1.3 stylesheets are fully conformant. All I want to know is whether this problem happens in a standard install of PunBB. If it doesn't then its related to mods so it isn't a bug.

it's not related to mods - it has to do something with styles.
yes... on 95,84% it's caused by styles with fixed width. + attribut size in input elements

currently, the fastest fix which i found, is add this to style/imports/base_admin.css:

#adminconsole td input {width: 100%;}

it solves the overflow, but it has a lot of side effects.

i've tested this just with Zoey B&W style, but it should works with others... so try it.
btw, coxis, what style do you use?

iam afraid that a complete solution will need some deeper modifications. let's find out what...