I don't know when they discovered it, but I suspect it has long been known to the company. According to the Advair Web site, "The most common side effects observed with ADVAIR DISKUS were headache, oral thrush, musculoskeletal pain, throat irritation, lower viral respiratory tract infection, and hoarseness. Some people may experience increased blood pressure and heart rate, or changes in heart rhythm. The use of inhaled corticosteroids, like the one in ADVAIR DISKUS 250/50, may increase your risk of developing bone loss (osteoporosis)..."

Also, according to an article on this site, some studies have long shown that corticosteroids (which are used to reduce the inflammation in the lungs of asthmatics) may lead to a "higher risk for bone loss in patients who take inhaled steroids regularly, a side effect which is known to occur with oral steroids."

So, it's not a new discovery, it's a concern of using corticosteroids for a long time.

Dr. Fred Little wrote a SharePost about the safety of using steroids for asthma control. Click the blue text to read the whole thing.

Talk to your doctor is you are concerned about bone loss. Your doctor may talk to you about things you can do to protect your bones, if necessary, including weight training, eating more foods rich in calcium and Vitamin D or taking supplements with those nutrients.