2.1.1295 Part 1 Section 188.8.131.52, round (Round Line Join)
a. The standard states that line joins will be round.
In Office, the following preset shapes ("[ISO/IEC-29500-1] §184.108.40.206; ST_ShapeType (Preset Shape Types)") will use a mitered line join ("[ISO/IEC-29500-1] §220.127.116.11; 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