Those bugs could not be fixed without changing the behavior. The problem was that we stored the old topMargin and set that back when a flickable was unset from the Header. However, there are cases (even in our UITK gallery, outside of our control depending on the QML engine) when Header instances are destroyed and/or (un)set the flickable property, there may be different headers setting conflicting values for the same Flickable.topMargin.
Also it was requested (Andrea initially brought it up I think) to not undo an existing flickable.topMargin that an app sets, but instead simply add the Header height to it. We don't have a bug report for that though.
Those bugs could not be fixed without changing the behavior. The problem was that we stored the old topMargin and set that back when a flickable was unset from the Header. However, there are cases (even in our UITK gallery, outside of our control depending on the QML engine) when Header instances are destroyed and/or (un)set the flickable property, there may be different headers setting conflicting values for the same Flickable. topMargin.
Also it was requested (Andrea initially brought it up I think) to not undo an existing flickable.topMargin that an app sets, but instead simply add the Header height to it. We don't have a bug report for that though.