The problem here is that IWD2 refuses to treat AREA variables as AREA variables unless they have the form ARxxxx with x in [0-9]. I have tried for a bit and absolutely cannot come up with a "happy renaming scheme" (e.g., _r0502, a_0502, ab0502, ar05020, ar0502_, ...) that works.
I had hoped that prepending GLOBAL would work but I forgot about the special (and, IMHO, a bad design choice) "undefined until visited" semantics.
However, I cannot use BG2 areas as is. That would break my goal of not destroying IWD2 *and* it would make it difficult to start the game (the gov't district would override the targos docks, yada yada) *and* bits of the engine I don't really care about (either built in or in 2da files) already make assumptions about areas with those names.
So with a heavy heart I will remap all BG2 AREs in sequence starting with AR0000. This works fine (I have tested it) and is transparent to players but is annoying for testers.
If you can think of something better, let me know. Fixed in v6.