search case works, simple case doesn't

[hespora]

Cognos 10.2.2 on Oracle...

in a query, i'm inserting a simple mapping:

Code Select Expand

case
  when [dimension] = 'value' then 'blah'
  else 'blub'
end
That one works fine. Replacing the syntax with a simple case however:

Code Select Expand

case [dimension]
  when 'value' then 'blah'
  else 'blub'
end
will fail to run and yield an ORA-12704 character set mismatch. My [dimension] on the db is of type NVARCHAR; the only thing I can think of here is that search case and simple case use different data types for interpreting  the literals - is that what is happening?