Weird Opera behavior with CSS border property

I've got such annoying thing when using border property for button:
when I click on the button, which border is defined in CSS (i.e. not 'none' and has some width - 1px or more) I see some ghost rectangles appearing in certain areas of the page. These rectangles are just a garbage on screen, coz when I resize the page or make some other things like clicking on other button, it disappears...

What's that and how can I beat it?

do you have an example or some code that we can look at?

Yes, please:

Here is what written in my style.css:

input.stagebutton {
height: 50px;
width: 100px;
background: #DDDDDD;
border: 1px solid #000000;
font-weight: bold;
}

and here is use of stagebutton class:


....
<td width="100"><input type="button" name="btnPP" value="Preprocessing" width="100" height="50" class="stagebutton" onClick="clickStage(this)" onMouseOver="maybeChangeCursor(this)"></td>
....

Hmm, weird thing... I've tried the code on more old Opera - 7.11 vs. 7.23 and didn't meet this problem.
But I want the code to work on every Opera browser.

What it could be?