Bison: Production ignoring required syntax - grammar

Question

I have the following rule in my .y file:
statement:
expression |
REDUCE operator reductions ENDREDUCE |
IF expression THEN statement_ ELSE statement_ ENDIF |
CASE expression IS cases OTHERS ARROW statement_ ENDCASE
;
cases:
case cases |
;
case:
WHEN INT_LITERAL ARROW statement_
;
The cases statements is a list of case statements. After the cases, the OTHERS ARROW statement_ portion is required as a default (like switch/case in programming) before the ENDCASE token. However, when testing it, it does not think it is a syntax error for not having it:
./compile < tests/syntax5.txt
1 // Multiple errors
2
3 function main a integer returns real;
syntax error, unexpected INTEGER, expecting ':'
4 b: integer is * 2;
syntax error, unexpected MULOP
5 c: real is 6.0;
6 begin
7 if a > c then
8 b + / 4.;
syntax error, unexpected MULOP
9 else
10 case b is
11 when => 2;
syntax error, unexpected ARROW, expecting INT_LITERAL
12 when 2 => c;
13 endcase;
14 endif;
15 end;
Lexical Errors: 0
Syntax Errors: 4
Semantic Errors: 0
Duplicate Identifier Errors: 0
Undeclared Errors: 0
Total Errors: 4
Did i set something up wrong?

Answer 1

Sorry, it was error recovery. I added error ';' to the case rule:
case:
WHEN INT_LITERAL ARROW statement_ |
error ';'
;
And now see the error:
1 // Multiple errors
2
3 function main a integer returns real;
syntax error, unexpected INTEGER, expecting ':'
4 b: integer is * 2;
syntax error, unexpected MULOP
5 c: real is 6.0;
6 begin
7 if a > c then
8 b + / 4.;
syntax error, unexpected MULOP
9 else
10 case b is
11 when => 2;
syntax error, unexpected ARROW, expecting INT_LITERAL
12 when 2 => c;
13 endcase;
syntax error, unexpected ENDCASE, expecting WHEN or OTHERS
14 endif;
15 end;
Lexical Errors: 0
Syntax Errors: 5
Semantic Errors: 0
Duplicate Identifier Errors: 0
Undeclared Errors: 0
Total Errors: 5