min ( distinct ) over ( ) returns wrong value

select TDEC.CDEC, min( distinct TDEC.CDEC ) over () from TDEC 

CDEC	min( distinct TDEC.CDEC ) over ()

<null>	-1

-1	-1

0	-1

1	-1

0.1	-1

10	-1

select `tdec`.`RNUM` AS `RNUM`,`tdec`.`CDEC` AS `CDEC` from `tdec` 

select VDEC.CDEC, min( distinct VDEC.CDEC ) over () from VDEC 

CDEC	min( distinct VDEC.CDEC ) over ()

<null>	10

-1	10

0	10

1	10

0.1	10

10	10