While you enter a transaction, GC tries to sort the splits "debits before credits", what usualy works fine.

On the other hand, GC acts different, depending of your key pressed at the end of the line.

If you enter first a credit split the behavior is somtimes confusing:

<tab> moves you to the next split without sorting as "the normal user" would expect.
<enter> insert an new, "imbalanced" split as line 1,
   keeps your credit split to line 2 and
   moves the cursor in line 3.

Now it depends on what you do next. 
You can end up with 
  an only not so nice looking txn with an additional $0 imbalanced split 
  or more worse things, as watched e.g. as one part of the user confusion in bug 433081, if other things also do not work as expected.

So my suggestion would be: wake up the user by popping up a warning, if a transaction contains imbalanced or orphaned splits. 

This could be done by the standard "Save the changed transaction?" dialog with some other texts.