2.1.1305 Part 1 Section 20.1.8.52, round (Round Line Join)

a.   The standard states that line joins will be round.

In Office, the following preset shapes ("[ISO/IEC-29500-1] §20.1.10.55; ST_ShapeType (Preset Shape Types)") will use a mitered line join ("[ISO/IEC-29500-1] §20.1.8.43; miter (Miter Line Join)") even if round is specified:

cube, moon, chevron, ellipseRibbon, ellipseRibbon2, plus, rightArrow, stripedRightArrow, notchedRightArrow, leftArrowCallout, leftRightArrowCallout, upDownArrowCallout, quadArrowCallout, star4, star5, star8, star10, star12, star16, star24, star32, upArrow, downArrow, upDownArrow, leftUpArrow, bentUpArrow, mathPlus, mathMinus, mathMultiply, mathEqual, mathNotEqual