"[" is not classed a unicode character http://en.wikipedia.org/wiki/List_of_Unicode_characters (my guess) as to why this wouldn't work:
declare @v nvarchar(255)
set @v = '[x]825'
select 1
where @v like '[x]825'
[]
defines a range of characters for a pattern match. It has special meaning in a LIKE statement. Here's the documentation for it.
If you're looking for those characters explicitly, you'll need to escape them, like this:
declare @v nvarchar(255)
set @v = '[x]825'
select 1
where @v LIKE '![x]825'
ESCAPE '!'