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
variouspoints in the code 
similar to the following:

Unable to create new submission. org.apache.commons.dbcp.DelegatingPreparedStatement@180b22ejava.sql.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
thecode, 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
toprocede 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,
newversion, etc).  I 
am using build 311 of the driver.