Execution logs, which are generated by logging code, are widely used in modern software projects for tasks like monitoring, debugging, and remote issue resolution. Ineffective logging would cause confusion, lack of information during problem diagnosis, or even system crash. However, it is challenging to develop and maintain logging code, as it inter-mixes with the feature code. Furthermore, unlike feature code, it is very challenging to verify the correctness of logging code. Currently developers usually rely on their intuition when performing their logging activities. There are no well established logging guidelines in research and practice. In this paper, we intend to derive such guidelines through mining the historical logging code changes. In particular, we have extracted and studied the Logging-Code-Issue-Introducing (LCII) changes in six popular large-scale Java-based open source software systems. Preliminary studies on this dataset show that: (1) both co-changed and independently changed logging code changes can contain fixes to the LCII changes; (2) the complexity of fixes to LCII changes are similar to regular logging code updates; (3) it takes longer for developers to fix logging code issues than regular bugs; and (4) the state-of-the-art logging code issue detection tools can only detect a small fraction (3%) of the LCII changes. This highlights the urgent need for this area of research and the importance of such a dataset.