Thank you for your interest, Aditya. The error was kindly fixed by Hans
introducing the following fix at line 993 in
tex/texmf-context/tex/context/base/mkxl/back-exp-imp-mth.lmt:

function extras.msubsup(di,element,n,fulltag)
         local data = di.data
         local nuc = found(data)
         local sup = found(data,"sup")
         local sub = found(data,"sub")
         data[1] = nuc or dummy_nucleus
         data[2] = sub or dummy_nucleus
         data[3] = sup or dummy_nucleus
         data.__i__ = 3
         local sp = specifications[di.fulltag]
         if attributes then
             attributes.mathsupindex = sp.supshifted
             attributes.mathsubindex = sp.subshifted
         else
             di.attributes = {
                 mathsupindex = sp.supshifted,
                 mathsubindex = sp.subshifted,
             }
         end
     end

This solved the issue.

-- 
Andrés Conrado Montoya
Andi Kú
andresconrado@gmail.com
http://sesentaycuatro.com
http://messier87.com
http://chiquitico.org
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Los fines no justifican los medios, porque la medida verdadera de nuestro
carácter está dada por los medios que estamos dispuestos a utilizar, no por
los fines que proclamamos.
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“You develop an instant global consciousness, a people orientation, an
intense dissatisfaction with the state of the world, and a compulsion to do
something about it. From out there on the moon, international politics look
so petty. You want to grab a politician by the scruff of the neck and drag
him a quarter of a million miles out and say, ‘Look at that, you son of a
bitch.’” — Apollo 14 astronaut Edgar Mitchell