Hopefully I can describe this correctly. It's really annoying. It hasn't always done this, so I'm not sure if I accidentally remapped a keystroke or changed some setting. Using 2016.1.3 on OS X with default 10.5+ keymap.
Suppose I have a small block of code like this:
When I hit alt+enter it correctly brings up the suggestions and you can see "Insert new" is highlighted:
However, when I hit enter here, it does not select "Insert new" it just inserts a newline into the editor where my cursor was:
Any ideas? This happens with anything that pops up like that as a tooltip/suggestion. Enter just inserts a newline.