When changing timezones in Windows, or when the "daylight saving" time changes, Notepad++ believes that any open files have been changed and asks if you want to reload. This is obviously a side effect of the way that N++ does not lock files when they are open, but it can cause confusion and potential data loss (if the user has made changes but answers "yes" to reload).
N++ should be able to "catch" timezone changes and decide whether a file has really been modified.
This has been happening as long as I can remember - it is not a new bug! It is a significant annoyance for anyone who travels regularly.