Cache.Add absolute expiration - UTC based or not?

Question

The examples for Cache.Add uses DateTime.Now.Add to compute the expiration, i.e. it passes:

 DateTime.Now.AddSeconds(60)

as th

Answer 1

Cache.Add converts the expiration date to UTC before storing it.

From Reflector (I've omitted most of the parameters to make it easier to read):

public object Add(... DateTime absoluteExpiration ...)
{
    DateTime utcAbsoluteExpiration = DateTimeUtil.ConvertToUniversalTime(absoluteExpiration);
    return this._cacheInternal.DoInsert(... utcAbsoluteExpiration ...);
}

In CacheExpires.FlushExpiredItems, utcAbsoluteExpiration is compared to DateTime.UtcNow. As Joe notes in his answer, this causes unexpected behavior when a cache item's addition and expiration span the end of daylight saving time.