Hi Robert and thank you for being our longtime fan!
MySQL plugin is brand new in Toad Extension for Eclipse. I personally couldn't reproduce your particular problem (maybe I didn't try enough). But we know about issues in the Data tab that are complex and will need some debugging. So, stay with us and we will try to get it right till the next release.
this bug is fixed in 1.6.1 which is about to be released. We handled the exception and decided to represent that "zero" value as null (because it is used in MySQL as dummy value). We are looking for further feedback from MySQL users!