UTC to local time problem

From openweathermap.org I get a UTC time string value like this:

"2017-02-20T11:09:02"

This will is stored in an item:

DateTime Weather_Last_Update_UTC “Letztes Update [%1$td %1$tb %1$tH:%1$tM]” {http="<[weathercache:60000:XSLT(openweathermap_lastUpdate.xsl)]"}

Viewing this item in the sitemap shows 11:09 but it should be 12:09 in my local time. Then I noticed that the +1 hour timezone change for my country is already added if you output the UTC item as string:

logInfo("Weather","Weather_Last_Update_UTC changed:" + Weather_Last_Update_UTC.toString)

Weather_Last_Update_UTC changed:Weather_Last_Update_UTC (Type=DateTimeItem, State=2017-02-20T11:08:28.000+0100, Label=Letztes Update (UTC), Category=null)

But why isn’t the extra hour added in the sitemap view?