variable not found in subplan target list?

I've got the message "ERROR: variable not found in subplan target lists"
when I have a union between 2 views. Both selects from the views run
without the union. Same result using intersect and except. Same result
using any of them with the all qualifier. Explain of the union gives
the error, explain of each individual select gives a result.

The view definitions contain unions and cross joins.

The error still occurs if I simplify the selects down to

select 'abc' from view1
union
select 'cba' from view2

"PostgreSQL 7.4 on i686-pc-linux-gnu, compiled by GCC 2.96"
redhat 7.2 (2.4.7-10)

klint.

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