Alternator mask issue

[MadMat1]

I have a problem trying to use two masks together with the alternator operator.
They work fine on their own but there are odd behaviours when joining.

I'll try to explain using this jsfiddle.

The first two masks works as they should, but in the third if you do this then the characters won't erase as they does in the first mask field:

• Type "12345678A"
• Move cursor to the position where number 6 is.
• Hit backspace several times.

Am I using the alternator operator in the wrong way?
Thanks in advance.