With SHORTANSWSER, the teacher should not have any of the following two-character sequences in the answer: %# %~ %} %= =# =% =} =~ ~# ~} and ~~, because there should be no empty answers or empty answer options. However, the teacher may inadvertently write these sequences.
The problem is that validation treats these two-characters sequences as if the second character were escaped* and thus gives unexpected results. The teacher may have trouble understanding what is happening.
* This can be considered as a bug.
- Identify these two-character sequences and interpret them as empty answers.
- Give the following message: "The sequence %# (or %~, etc.) is illegal, an answer can not be empty."