Upgrade to pg and driver version 8.x code compatibilities

We've upraged out development and qa servers to postgresql 8. When using our java application, we get errors at various points in the code
similar to the following:

Unable to create new submission. org(dot)apache(dot)commons(dot)dbcp(dot)DelegatingPreparedStatement(at)180b22ejava(dot)sql(dot)SQLException:
ERROR: column "job_experience" is of type smallint but expression is of type character varying

If I downgrade the driver to the 7.4.x version the error goes away and we can run the application.

I realize this is probably pointing to bad coding practices, which will be fixed, I believe, as our developers work on the code, but we want to
avoid an all out push to get the code all fixed (similar problems exist in a *lot* of places in the code). We'd like to procede with
upgrading to 8.x server -- Two questions arise

1. What changed between the driver versions that generate this error?

2. What is the downside of continuing to use the 7.x version of the driver -- or are there better alternatives (patch, new version, etc). I
am using build 311 of the driver.