Which version of InDesign and which OS?
And which enter key? The one on the number pad is the default shortcut for a column break and would send you into overset if there is no next column.
I have cc 2014 and Mac OSX 10.9.5
it's not the one on the number pad
Try resetting your InDesign preferences:
Close InDesign and relaunch it, and IMMEDIATELY hold down Ctrl + Alt +
Shift (Windows) or Cmd + Ctrl + Opt + Shift (Mac), and respond with Yes to the dialog asking if you really want to replace the
If you aren't asked the question, you didn't hold down the keys quickly enough!