  Software developers attempt to reproduce software bugs to understand their
erroneous behaviours and to fix them. Unfortunately, they often fail to
reproduce (or fix) them, which leads to faulty, unreliable software systems.
However, to date, only a little research has been done to better understand
what makes the software bugs non-reproducible. In this paper, we conduct a
multimodal study to better understand the non-reproducibility of software bugs.
First, we perform an empirical study using 576 non-reproducible bug reports
from two popular software systems (Firefox, Eclipse) and identify 11 key
factors that might lead a reported bug to non-reproducibility. Second, we
conduct a user study involving 13 professional developers where we investigate
how the developers cope with non-reproducible bugs. We found that they either
close these bugs or solicit for further information, which involves long
deliberations and counter-productive manual searches. Third, we offer several
actionable insights on how to avoid non-reproducibility (e.g., false-positive
bug report detector) and improve reproducibility of the reported bugs (e.g.,
sandbox for bug reproduction) by combining our analyses from multiple studies
(e.g., empirical study, developer study).
