Bold text is input, plain text is the program's reaction.
[rtn] is the return key.
Note: the actions Forth normally takes after an error will be suppressed.

EX [rtn]
0: [ DROP [rtn] -4 THROW executes
0: [ 12 [rtn]
1: 12 [ 1999 [rtn]
2: 12 1999 [ : ZWAP [rtn]
2: 12 1999 ] QWERTY [rtn] -61 THROW executes

EVALUATE can't grok QWERTY -- this is neither a word nor a number. However, compile-state is kept intact, as is the stack.

2: 12 1999 ] 2>R [rtn]
2: 12 1999 ] R> R> [rtn]
2: 12 1999 ] ; [rtn]

Notwithstanding the error, ZWAP seems to have been compiled.

2: 12 1999 [ ZWAP [rtn]
2: 1999 12 [ ' ASDF [rtn] -13 THROW executes

TICK can't find ASDF.

2: 1999 12 [ -56 THROW [rtn]
[rtn]  ok
.S [rtn] ( 1999 12 )  ok

EX enters an infinite loop which you only can break out of by using QUIT or BYE. Of course BYE is inappropriate. -56 throw is a special THROW that executes QUIT.
Also try ABORT and TRUE ABORT" Hello!"
ABORT should execute -1 THROW. Some Forths allow ABORT" in interpretation state and execute -2 THROW.