In all the following tests the red box has position:relative. To check its rendering it is sandwiched between two boxes (grey, zero margins, static position.)

 
This is a box with position:relative
 

With a slightly bigger than normal line height. In IE7-/Win the relative box is not fully rendered in the top part: there is a white stripe between the first two boxes.

 
This is a box with position:relative
 

with border

 
This is a box with position:relative
 

With a bigger line height. The problem is more evident.

 
This is a box with position:relative
 

with border

 
This is a box with position:relative
 

with margins

 
This is a box with position:relative
 

With hasLayout on the relative box, the problem disappears.

 
This is a box with position:relative
 

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