Right now if you R click > Data > Export Data for a selection layer with a definition query, the exported feature class ignores the definition query. This is unexpected since non-selection layers with a definition query do respect the definition query on export. There's also no warning that your exported layer will have more features not seen in the original layer. Please respect both filters when exporting features from a selection layer with a definition query.
These things should really be tested more rigorously -- by humans -- before release. I feel like I run into an issue like this in Esri software several times a day.