Hebrew "falling back" in Microsoft applications


Hi, all. Long time lurker, first-time poster. I'm working on a font project that includes an integrated set of Hebrew characters (actually, the project started out as a Hebrew font that grew to include a harmonious Latin script). Recently, the Hebrew characters (including the Shequel, but none of the other currency symbols) began "falling back" to TNR or some other default font, but only on Microsoft applications, including Word and Character Map. Other, non-Microsoft applications display the Hebrew characters correctly. I've done nothing to the OpenType script or any of the other "under the hood" stuff; I've just been drawing contours, adjusting bearings, etc. as I have been all along. Any idea what's triggering this?