We have a similar issue and I believe it is to do with the underlying short date format of the operating system when using Windows Integrated Authentication to identify users.
We are running with English (United Kingdom) for our regional settings. Setting short date format to dd-mmm-yy results in all date fields being checked and set to 1/1/99 as the date the event occurred (apart from the date found field where we explicitly set to today's date as a default value). If I change the system short date format to dd-mmm-yyyy then the date fields behave as expected (not checked, but showing today's date).
We are running version 7.0.1.7150