I've had the same issue in HKG with two different hotels (not Accor affiliated) both were booked on "flexible" rates and guaranteed with a credit card.

A week after making the bookings, I was sent an email from their reservations department asking to take a "deposit" of one nights stay in order to "guarantee" my booking...

Having been a hotelier in a previous life I'm well aware of the difference between deposits and guarantees and what each of these mean.

The excuse given to me by the hotels was exactly as above that it was a busy period, I explained to reservations that no where did it mention that a deposit would be taken and that I had chosen the "flexible" option because of the need for flexibility in being able to cancel my bookings due to unforseen changes.

After a bit of too-ing and fro-ing, I replied that they could take the deposit within 48hrs of my arrival as by then the likelihood of changes to my schedule would be minimal.