Has anyone else noticed some unexpected behavior with the latest version of the Data Loader, version 21.0?  Here is a list of just some of the issues that I've come across that do not occur when using previous versions of the Data Loader:

1. When attempting to update a small subset of fields contained in the .csv file but not all (ie. mapping only a few fields), the Data Loader throws an the Error:  Failed to find mapping for '<one of the unmapped fields in the .csv file>'.  However, if all the fields in the .csv file are mapped, it appears to work correctly.  Previous versions had no problem with mapping only a subset of fields contained in the .csv file, my guess is this is a bug.
2. After successfully completing an Export, the Data Loader stops responding to any action button click for Insert, Update, Upsert or Delete.  However, it will let you choose Export or Export All.  I cannot tell if this one is a new "feature" or a bug.