Well I did some maths and I bought lvl 3 for 0.1BTC
I should get 0.000015BTC/min in the end it is always less.
Are you following the slider? I have noticed that my "counter" is half as slow as the slider, making me update the page after 8 minutes with 600 and not 1200 that i should have (level 1)
Can you PM the OP about this? Or maybe he will see. This is definitely a problem, the site should be working properly.