Wrinkled bulbs

[Pupka]

Hi, I'm a newbie here and your patience is very appreciated!

Recently I bought a third orchid from oncidium alliance and they all have the same problem: very wrinkld bulbs. The thing is that when they arrive there is nothing wrong with their bulbs -- they are very stuffed and round. But on the next day already the bulbs get wrinkled. I suppose it's something to do with humidity, but my orchids grow in bathroom and humidity level there does not drop below 40%. Is it still not enough for them?
Same problem with cattleyas, too.