In a container (the light gray box with striped background and border) there is a box with a margin-top. In IE7-/Win this is ignored if the box is preceded by an absolutely positioned sibling. In IE7 this happens also when the box is preceded by a fixed positioned one.
If the box precedes the absolutely positioned one the problem does not occur.
position:relative on the container (and/or on the inner box with the margin-top) has no effect on the problem.
In the above cases both the container and the static box have hasLayout. Presence/absence of hasLayout causes many similar problems with nested boxes: IE7- wrong collapsing, disappearing of margins and hasLayout. The current problem does not occur if the static box does not have hasLayout, but of course this is a rarely usable fix.