The starting point is that any UDF starting with 2 underscores is considered an internal UDF and will not be colored/recognised unless it exists in the same file.
This means that the FAST search using the tables will work in wdcore.au3, but not in any other file, even when there is an include.
Having said that, I agree it should then try to old "long route" which opens the current included files and check for the UDF, which indeed wasn't working correctly.
That last part is fixed in the latest version included in the ZIP.