I encountered a strange bug before, and now I have more time, so I want to record it.
It's a bug about a calendar control.
Click on the group period, and the pop-up window of the calendar control will pop up. The interface display of the control is probably like this: the first row is the day of the week (arranged from Sunday to Saturday, this part is written by the developer), and then the following is the date of the calling system. Detailed description of the bug: Change the system language, such as changing to English (UK), assuming that today should be Thursday, after changing the language. Today is Wednesday.
The reason is: for the US, Sunday is the first day of the week, and for the UK, Monday is the first day of the week, so after changing the language, the above bug occurs. Later, the developer modified the code without writing the day of the week to death, and the problem was fixed.