The bug-fixing process requires software maintenance resources. Usually, defects are submitted, fixed and closed, but sometimes they have to be reopened because of a change of resolution. It happens when a defect was evaluated incorrectly at the beginning. This problem can increase maintenance costs and software quality in general. In this paper, we investigate the characteristics of such defects and their bug reports and call them “underestimated”. Our research is based on general statistical indicators and text descriptions of defect reports. We propose using different methods of feature selection and ranking in order to reveal the significant terms of such defects. The top of significant terms of the underestimated bug reports can help to find the root causes of such life cycles.