Fabio,
I was reading the help file and the CAST Conversion from Character to Datetime is not Full but Partial.
You can get what you want this way:

t=DATETIME()
SET CENTURY OFF
?CAST(m.t AS D)=CAST(CAST(m.t AS C(8)) AS D)

or

t=DATETIME()
SET CENTURY ON
?CAST(m.t AS D)=CAST(CAST(m.t AS C(10)) AS D)

Peter

thanks Peter, i have not problem to found a workaround.

The problem is conceptual.