Here's the response I got...
****************************************
When you define a map id with a minus sign ("-"), it is
purposely blocked. Defining of MapId results in generation of a
header file (.h file), which is included by the developers in the
code. Now in some languages, like C, C++, minus signs ("-") are not
allowed to be used in #define statements. In order to prevent this
problem, minus signs ("-") have been purposely been not allowed in
defining the Map Ids.
****************************************
I am guessing that It should not have worked in RH5 and it
has been blocked now to avoid the issues.
Help others by clicking Correct Answer if the question is answered. Found the answer elsewhere? Share it here. "Upvote" is for useful posts.