Change in 9.1?

Hi,

we have a reporting tool, that sometimes uses this kind of condition.
...WHERE a.field = a.field

To explain this: a.field can be filtered by the user. the user can choose
some values. if he does, this condition will be build:
...WHERE a.field IN (1,2,3)

If the user doesn't choose any values the * = * condition is used.

Since 9.1 we're experiencing problems with this construction. Have there
been any changes to the planner regarding this?

Ty
Regards, Jasmin