I'm currently developing an OpenType font that contains two sets of figures -- Lining Proportional figures as the default and Lining Tabular figures activated with the "tnum" feature.
The Lining Tabular glyphs are named in Adam Twardoch's suggested form of "number.lnum_tnum" and are in the class "@FIG_TAB_LINING", the Lining Proportional figures are in the class "@FIG_FIT_LINING" but the problem also occurs without using classes.
The problem is that InDesign labels the glyphs in the tnum feature as being both tnum and onum even though there is no onum feature in this font. This is to say that in the Glyph palette rolling over the Tabular glyphs shows that they are "Tabular Figures (tnum) + Oldstyle Figures (onum)", and the OpenType submenu of the character palette gives the option to select "Tabular Oldstyle".
I understand that the pnum and tnum features are modifiers for lnum and onum (applying tnum could change lnum_pnum and onum_pnum to their tabular counterparts), so I'm not sure if there's a way that I can or should specify that the glyphs in the tnum feature are *only* lining, and never oldstyle.
To fix this problem I've tried adding an onum feature with a different set of glyphs in from font with the idea that it might draw InDesign's attention away from thinking the tnum group could contain oldstyle figures. I've also switched to using the tabular figures as the default and creating a pnum feature instead, but this ends in the same result of InDesign thinking that the glyphs are both proportional lining and oldstyle.
I've been able to reproduce this in more than one font and I'm using FontLab 4.6 on the Macintosh.
Has anyone else see this? Any thoughts would be much appreciated!