This problem is the ambiguous name between Windows True Type font RomanS (romans__.ttf) and AutoCAD SHX font romans.shx. I hope Autodesk will fix this text style name issue in next releases.
AutoCAD shows RomanS true type font as the same name romans.shx of SHX font in the Text Style dialog. So if there are two TTF and SHX fonts that have the same name, the SHX font name will show on AutoCAD, and TTF font name is invisible.
Both two fonts look similar, except RomanS is thicker than romans.shx. This has been confusing users for years why the same font name but have different thickness. In fact, they are two different fonts (in different text styles) but wearing the same name!
To archive the “blank” font style instead of Regular, you should change the true type font RomanS (it’s invisible in AutoCAD) to the real SHX font by code. Without writing code, on AutoCAD Text Style dialog, we can do a trick to change the font name romans.shx (of TTF thick font) to any font and then reverse it back. It will remove the TTF font and get the correct SHX font. We also need to run REGEN command for the drawing to display updated text styles.
-Khoa