As others have reported, and the maintainer/author has indicated this is a result of XP presentation of timestamps during daylight savings time.
I appreciate the low level cause of the usability problem is Windows.
But from a usability perspective, a workaround would be greatly appreciated. I sync thousands of files, and I look for the unexpected update to notice that a file has changed inappropriately.
If a few thousand files report as out of sync, I can't manually decide on each one if they should be updated or not. Unfortunately it makes WinSCP somewhat irrelevant for my situation. That's disappointing as it's an important tool.
I hope the author will consider making changes to WinSCP to improve it's usability in a mixed windows scenario. I will update away from XP at some point, but for now that's not practical.