Exporting SSRS report to Excel
There is some Technet information on the intended behaviour of the export: https://technet.microsoft.com/en-us/library/dd255234(v=sql.105).aspx


  Images, charts, sparklines, data bars, maps, gauges, indicators, and
  lines are positioned within one Excel cell but they sit on top of the
  cell grid. Lines are rendered as cell borders.