Moin,
if I removed tags it wasn't intentional. I have no idea why the tags disappeared. What I know is that the data (shape and position) of the roads in this area of Japan are provided to OSM by the IT company "YAHOO". (https://wiki.openstreetmap.org/wiki/YahooJapanALPS_Data)
It's possible that the "yh:" tag stands for the data provided by Yahoo and automatically disappears when a user modifies the objects (in this case Yahoo's streets).
Thanks for the hint
Tschüs