Problem with the number of the denominator in the fractional part

Hello. Instead of a thousand words, watch this short video. Many thanks.
Fractions_test.zip (4.79 MB)

The OpenType dialog uses the / as an escape character. If it is followed by some numbers it will interpret this as a character code-point.
OpenType Fraction Preview 2.png
Use an additional // to get the expected behaviour.
OpenType Fraction Preview.png