It looks like you accidentally enabled the OpenType feature "Ordinals".
Why are only the characters 'o' and 'a' superscripted, and not the entire text?
The function of ordinals is different from superscript:
Function: Replaces default alphabetic glyphs with the corresponding ordinal forms for use after figures. One exception to the follows-a-figure rule is the numero character (U+2116), which is actually a ligature substitution, but is best accessed through this feature.
Example: The user applies this feature to turn 2.o into 2.º (abbreviation for secundo).
(Microsoft OpenType specification, https://www.microsoft.com/typography/otspec/features_ko.htm#ordn)
Some fonts contain properly drawn superscript characters to support proper ordinals for the most frequent English ordinal indicators "st", "nd" and so on, to enable "1st", "2nd" – more rare fonts do not assume English only and contain the entire lowercase alphabet.
Minion Pro contains è so one can typeset "2ième" with confidence. (The accented character may be meant for another language and number. If you look this up you may find "the only correct abbreviation for deuxième is 2e".)
Most font designers don't go that far. But as the specific characters 'ª' (feminine ordinal indicator, Unicode U+00AA) and 'º' (masculine ordinal indicator, Unicode U+00BA) are part of the recommended basic supported character set "Latin-1", they usually appear in fonts anyway. From that, it's a small step to add the feature 'ordinals', because its most basic form is to only swap 'a' for 'ª' and 'o' for 'º'.