Comment 3 for bug 1658029

I found a workaround and something between a workaround and a solution.

workaround:
-open the document properties dialog
-change document units to "px"
-set the scaling factor x to 1.0
-change the docoment unit back to the unit you want
-->superscript and subscript work as expected for any further use of the superscript and subscript buttons in this document

partial solution:
-in the document template the viewbox parameters must be set in inkscape units (px) not in "mm" or something else
-goto "installation path"\Inkscape\share\templates
-change within the default or another template e.g. "default.de.svg" the line for viewbox to contain dimensions in px units
-for an A4 template this means viewBox="0 0 793.7007874 1122.519685">
-->superscript and subscript work as expected for new documents based on this template

a real solution would be:
the size of superscript and subscript should be decoupled from the scale-x factor and solely depend on the underlaying font size