Artefacts in drawing histogram with "bars same" option

gPad->RedrawAxis();

See: http://root.cern.ch/root/html/TPad.html#TPad:RedrawAxis
or the “Drawing second THStack covers axis” thread: [url]Drawing second THStack covers axis

BTW. you can “EDIT” your posts, and so you can also replace attached pictures. No need to post/create a new message.