[NTG-context] vertical square root upstroke (instead of having a slant)

With the following minimal file on MkIV (2013.05.28 00:36 MKIV current), the upstroke of the square root is vertical instead of having the usual slant toward the right. With MkII it has the usual slant. I see this problem only with certain arrangements of variables (that recur often in my book chapter on springs and piano strings). For example, it goes away after changing the "\rho" to a "b". \starttext \startformula \sqrt{Tb^2\over \rho}. \stopformula \stoptext I know that the big math symbols are constructed differently in MkIV and MkII. Does the example above show an intended difference? -- -Sanjoy