lookupflag IgnoreMarks in FontLab not working in output font


I've been working on a mildly complex font for a client (moonlighting outside my day job).

I've never worked with using a lookupflag to ignore certain glyphs, but it seems like the perfect solution for a particular issue I encountered. So I tried to do it in FontLab. It compiled fine and I export the font, but the desired behavior is not occurring in InDesign CS5 (even when I set text with the WorldReady Composer active).

I'm wondering if I am doing something wrong, or...? Here's my process.

A) First, for the glyphs we want to be ignored, do the following in the FontLab glyph window:
- select the glyph.
- bring up the glyph properties dialog
- change the value of the OT popdown from "Unassigned" to "Mark"