  Students are able to produce correctly functioning program code even though
they have a fragile understanding of how it actually works. Questions derived
automatically from individual exercise submissions (QLC) can probe if and how
well the students understand the structure and logic of the code they just
created. Prior research studied this approach in the context of the first
programming course. We replicate the study on a follow-up programming course
for engineering students which contains a recap of general concepts in CS1. The
task was the classic rainfall problem which was solved by 90% of the students.
The QLCs generated from each passing submission were kept intentionally simple,
yet 27% of the students failed in at least one of them. Students who struggled
with questions about their own program logic had a lower median for overall
course points than students who answered correctly.
