macOS 10.14 Mojave on a MacBook Pro (Retina, 13-inch, Early 2015) Preview Version 10.1 (944.6.16)
Preview.app fails to adjust the font size of text entered in PDF text fields appropriately to the text field size:
The first screenshot is an already annotated PDF from a colleague with the last 2 text fields field added by them (with an appropriate font size scaling) and the first 3 fields edited by me, with wrong scaling. However, this also occurs on unedited PDFs as well.
Notice how it starts with correct scaling, and then glitches out, after I exit the text box.
Some mention the font settings of the text annotation tool. This seems to be ignored for text fields in PDFs however (set it to 3pt to test):
This problem occurred even before I updated to Mojave.
This only occurred with Preview on my Mac. Adobe Acrobat displays the values with appropriate scaling.