These tests show an unusual bug for Opera 9.1~9.5 when a container has a floated element with either in-flow block elements or inline boxes preceding or following it. Any bottom margin that borders the containers' bottom margin will be toggled on and of depending on the height of the float. If the height of the float is roughly equivelent to the height of the content beside the float within the container, then the bug can be toggled on and off by zooming in and out. This bug is remarkly similar to the IE/Win Margin Transference Bug in that it doesn't happen if the float is not being cleared.
<div class="container">
<div class="wrapper">
<!-- content here and/or -->
<div class="floatleft">div floated left</div>
<!-- here or enclosing the float -->
</div>
<div class="clear">Clear</div>
</div>
Passed: Gecko 1.7~1.9, Safari 3 & IE 5.5~7
Failed: Opera 9.1~9.5
Passed: Gecko 1.7~1.9, Safari 3 & IE 5.5~7
Failed: Opera 9.1~9.5
Passed: Gecko 1.7~1.9, Safari 3 & IE 5.5~7
Failed: Opera 9.1~9.5
Failed: IE 7 (due to the div enclosing the float having layout)
Please see another test by Bruno Fassino showing a similar bug affecting Opera 7~8 which has a space between a float and a clear.
Futher investigation with this bug.