I have exactly the same experience about the I love you mug as another review I just saw here.
I bought two mugs, one “I know” and one “I love you”. While the “I know mug” is labeled as handcrafted in Portugal with decent quality, the “I love you” mug is labeled as made in China and changed its color after dishwashing.
I like the design and it was supposed to be a present for my wife. I really disappointed by this and it made no sense for a 20 euro mug to have a quality lower than a 2 euro mug.

Update: the customer service has told me that the manufacturing of the mugs has been moved from Portugal to China. I think this cost cutting is the main reason for the bad quality of the products. I think the value of the brand should be quality crafted design goods, and now there is no reason to keep buying from them anymore.