I use ArcGIS 10.2.1 and I have the same problem. I'm using SDE datasets. Also, I have troubles with the "select by feature" function when I have joint table.
10.2.1 Shapefiles are unable to be spatially modified
here is something I asked about not too long ago. It may or may not have something to do with your issue. It's logged, but not fixed as far as I know. But if you are using Mapping and Charting, then that may be your issue.
This has been identified as a bug (NIM095455: In an edit session, snapping stops working on a layer if a join exists on that layer.) and has been fixed in 10.2.2