A relevant paragraph from the MtG Comprehensive Rules:
706.2. When copying an object, the copy acquires the copiable values of
the original object's characteristics
and, for an object on the stack,
choices made when casting or
activating it (mode, targets, the
value of X, whether it was kicked, how
it will affect multiple targets, and
so on). The "copiable values" are the
values derived from the text printed
on the object (that text being name,
mana cost, card type, subtype,
supertype, expansion symbol, rules
text, power, toughness, and/or
loyalty), as modified by other copy
effects, by "as . . . enters the
battlefield" and "as . . . is turned
face up" abilities that set
characteristics, and by abilities that
caused the object to be face down.
Other effects (including type-changing
and text-changing effects), status,
and counters are not copied. Example:
Chimeric Staff is an artifact that
reads "{X}: Chimeric Staff becomes an
X/X artifact creature until end of
turn." Clone is a creature that reads,
"You may have Clone enter the
battlefield as a copy of any creature
on the battlefield." After a Staff has
become a 5/5 artifact creature, a
Clone enters the battlefield as a copy
of it. The Clone is an artifact, not a
5/5 artifact creature. (The copy has
the Staff's ability, however, and will
become a creature if that ability is
activated.) Example: Clone enters the
battlefield as a copy of a face-down
Grinning Demon (a creature with morph
{2}{B}{B}). The Clone is a colorless
2/2 creature with no name, no types,
no abilities, and no mana cost. It
will still be face up. Its controller
can't pay {2}{B}{B} to turn it face
up.
I think that what this implies is that Sakashima does NOT become a 4/4 creature when copying a creatured-up Halcyon Glaze, but rather an enchantment with Halcyon Glaze's rules text. So you'd have to cast another creature to turn enchantment-Sakashima into a 4/4 flyer. I don't think he'd revert to being a 3/1 at end of turn; he'd stay a noncreature enchantment until returned to hand with Sakashima's ability.
Essentially the key issue here is about what the Magic rules like to call "copiable values". The switched-on Glaze is a valid thing for Sakashima to copy, because it's a creature in play, but its switched-on status is not a copiable value. So Sakashima just becomes a switched-off Glaze, with all the extra characteristics as defined in the Sakashima rules text.
