PDF forms: properties of text fields



I am am trying to configure bigger text fields with the following properties: "Font size = Auto" (which allows the font size to adapt, depending on the length of the text), and, for the same fields, "Allow Rich Text Formatting". However, if both these properties are selected, the function "Font size = Auto" does not work! I.e., the font size does not adapt. "Allow Rich Text Formatting" is deactivated, then "Font size = Auto" is working again.

But I need text fields which allow a variable length of text as well as text formatting (i.e. bold, italics, sub- and superscript). Any helpful information will be very much appreciated.