If people are buying houses, remodelling them and then selling, it is a normal and safe practice. It would be problematic if they had mortgages on the houses and couldn't pay them out, like during 2008. Okay, new flats are cheaper than the old ones. This is weird, but not bubbly, since low prices mean low demand, while bubbles are about very high demand for essentially empty offer. In my country real estate prices are lower now than they used to be about 5 years ago, but well-furnished new flats are obviously more expensive than the old ones.
The problem begins when too many people are trying to buy houses for rent or to swap and the market crashes. You're left with properties that nobody wants to rent out or buy, or in case of swaps nobody wants to pay you the price you expected and you have to pay the bills as the owner, so keeping the property on the market for years is going to bankrupt you.
Also, the demand might be decent now, but since average Joe is buying a property for rent, we'll at some point have dozens of people owning more than one property and trying to rent out, which won't probably end well for them as they will be left with properties that aren't making them money, but have to be maintained.
One factor that needs to be considered here is where the buildings are being built. From your case, I think people are buying the apartments in the outskirts of any given city and overtime people will start moving there and the rent/land value will go up.
Yes, those aren't downtown apartments. There are many factors to consider, one of them being construction materials. Older buildings are made of bricks, at least here in Europe. The newer ones are prefabricated and built within months. If you compare 50 year old buildings to the new ones, for the same price you're getting underground garages, terraces, huge panoramic windows, and cheaper per square meter than a 50+ year old downtown apartments.