It typically happens within the first year and is the result of imperfections in the glass.  

Also, you would not be painting the room with a flat paint, maybe a satin or semi-gloss, and hiding imperfections on reworked walls with a higher gloss paint is always a challenge.

There were some imperfections in the floor we did, but we weren't bothered by them as it's not a high end unit and we consider them to add character. =) Menard's recently started carrying an industrial concrete sealer so we went with that.

Infact, I dont know who said this first, or if Ill quote it correctly but"doing it, and doing it imperfectly, is much better than not doing it at all"

Vinyl flooring requires Luan ply under it otherwise all imperfections telegraph through the vinyl.

Humans are born different from one another and imperfectly and have to each seek his/her own balance.

The rigid core is more accepting of subfloor imperfections and is easier to install.  

It may also reflect a, more than typical, imperfect market.

The prices are more reasonable but the economic situation in these areas is still imperfect. 

This is a bit like selecting our politicians based on SAT scores - very imperfect, but at least you get the smart ones in office instead of the weird politicians that most democracies seem to have.But I do think they will face several shocks over the next few decades as they transition from a controlled economy to a free market.