Product Version: NetBeans IDE Dev (Build 201505020001)
Java: 1.8.0_45; Java HotSpot(TM) 64-Bit Server VM 25.45-b02
Runtime: Java(TM) SE Runtime Environment 1.8.0_45-b14
System: Windows 7 version 6.1 running on amd64; UTF-8; pl_PL (nb)

Write some code to have a hint in the editor. Call the hint with Alt+Enter (or Ctrl+1 if using Eclipse keymap like me). Change your mind and cancel the hint list with Escape - the list will disappear, but the Escape will begin an escape sequence (you can see an ESCAPE caption in the lower left corner of the IDE). Now press a key (for example an arrow key, "a" key or Escape again) - you will hear a warning sound and the key will not do any action.

Note it doesn't happen with Code completion list.

Testcase:

public class EscapeTest {

    public void demo() {
        String str = |
    }

}

1. While at the "|" position press Alt+Enter (you will see a "Split..." hint), then Escape (notice the ESCAPE caption), then "a" - you will hear a warning sound, and the "a" letter won't be added to the source code.

2. While at the "|" position press Ctrl+Space (you will see a CC list with many entries, starting with "toString"), then Escape (the list will disappear), then "a", and the "a" letter will be inserted as expected.