MAP IDs don't get recognized (Umlaut problem?)

(still RH 9 in this case - cannot switch easily)

I have a merged HTML Help project.

The single subprojects contain .h files with

#define Länge 1803

among others. In the single subproject all Map ids are listed (as blue icon).

In the merged central project (which includes the TOCs of the single subprojects)

exactly those MAP Ids which contain at least one Umlaut are missing (marked yellow).

How does the mechanism of merging the MAP Ids work? I also have one central .ali file which has been compiled together manually,

since the Redirect.1.htm:ms-its: thing was missing.

I'm clueless at the moment.

Any ideas welcome,

--

Christoph