You do not seem to understand how difficulty adjustments are performed. A pool does not "make" any network difficulty adjustments. The issues with "fake shares" and "shares below target", only affect the buggy pool itself and the miners on it, the network could not care less for these bugs.

The network, relying on DGW, makes adjustments based on the time that it took to solve previous blocks, and then estimating the nethash so that the new difficulty results in block solving at the desired rate.

Multipools hopping on and off are a well known problem. For a coin that has a modest nethash, when a multipool joins, difficulty will be through the roof. When the multipool jumps off, the network will have a hard time solving the next block. This is completely expected. Smart (or rather, ethical?) multipools, only jump on coins that have enough nethash to not be "catastrophically" impacted by the multipool. Does not seem to be the case with "trade my bit", but I honestly don't know of their motivations or if they care. No offense intended really.

Hope this helps settle your concerns.
Happy mining,
~ Myagui