There has been a good deal of debate over the recent study which found that people with a liberal political position give greater consideration to new data when processing information than conservatives, who tend to be more fixed. Critics contend that the study has no insight on which side is more likely to be correct. Basically, the argument comes down to schema reverberation.
When any kind of schema, whether it is an idea you believe to be true or a recognition that a black cube in front of you is your cell phone, becomes active in your mind, the schema reverberates. This prevents (inhibits) competing schema from also becoming active (if the cube is your cell phone, it can't also be your wallet; if I believe 2+2=4, I can't also believe 2+2=5). If I know the cube is my wallet, it makes less sense to search for more evidence than to engage in other thoughts. It is simply a function of opportunity costs v benefits.
We can interpret the study (if the data is valid) to mean that conservatives have stronger schema reverberation and more effectively inhibit the activation of competing schema. Once they become sure of an idea, they judge the value of spending their cognitive resources on other things to be greater.
So rather than liberals being more "open-minded" than conservatives, we can look at it as more of a difference in the allocation of resources. Liberals are more willing to reconsider their active schema whereas conservatives would rather use their cognitive resources elsewhere. Both situations have advantages and disadvantages.
What is interesting is how the difference maps to the conservative/liberal dimension. I could only conjecture, but it seems similar to the Myers/Briggs dimension of judging/perceiving. Judgers prefer to make a decision and stick to it (like conservatives) and Perceivers prefer to keep their options open (like liberals).