ERROR: assembler: Compiler limit exceeded while assembling user class; 255 fields allowed, 258 found

tested with SDK 4.1.3 :

1) create a class with exactly 253 user defined members:

class Test{
 var f1 as Toybox.Lang.Float?;
 var f2 as Toybox.Lang.Float?;
 [...]
 var f252 as Toybox.Lang.Float?;
 var f253 as Toybox.Lang.Float?;
}

2) compile results in error message:
ERROR: assembler: Compiler limit exceeded while assembling user class; 255 fields allowed, 256 found

issue 1:
Error message contains neither the impacted class nor the mc source file.

issue 2:
The 255 limit is not documented in any of the obvious places (e.g. CoreTopics or LearningMonkeyC)

issue 3:
There seem to be 3 hidden class members that reduce the actually useable count to 252.