When Isr is run from obs_lsstSim, the bounding box for some defects fall outside the bounding box of the mask that is being set. This problem was discovered when migrating to the new footprints API (the old API silently dropped anything outside the mask). The behavior and workaround can be seen in this commit: https://github.com/lsst/ip_isr/commit/b3afcd8d5702eb78aea2ca95e54b1683e93e5e4c. This ticket should investigate if the defect list is properly generated. The bit of code that is causing this failure is testLsstSimIsrTask.py in obs_lsstSim.