Code review is manual inspection of source code by developers other than the author. In a code review system, software developers submit code changes to fix software defects or add software features. Not all of the code changes will be integrated into the code base. Some of the code changes will be abandoned. The abandoned code changes could be restored for review, which allows contributors to further improve the code changes. However, it takes more time to review the restored code changes. This study collects 920 700 restored code changes from four open-source projects, investigates reasons for which code changes have been restored, uses thematic analysis method to identify 11 categories of reasons for restoring code changes, and quantitatively analyzes the characteristics of restored code changes. The main findings are as followings. (1) Among the reasons for which code changes are restored, the reason “improve and update” accounts for the largest proportion. (2) The distribution of reasons across the four projects are different, but the difference is not significant. (3) Compared with non-restored code changes, restored code changes have a 10% lower acceptance rate, 1.9 times more comments, and 5.8 times longer review time on average. (4) 81% of restored code changes has been accepted, while 19% of them has still been abandoned.