FL Forgets Plugin prsets?

It seems that I have some intermittent problesms - is it something I'm doing (not doing?)

1) Sometimes FL "forgets" the patch (Ins/Patch) loaded for a particular pattern and/or the instrument doesn't load at all (the name is there, but the instrument isn't), when i reload an old song. But sometimes it remembers.

2) when you load a second channel with the same instrument as a different channel (using a different patch), sometimes it wipes out the original assignment, sometimes not.

3) Sometimes the piano roll doesn't map all the sounds of a drum kit correctly (all the names are there, but only some of the sounds).

What's the general rule-of-thumb on how to use :
- The same instrument, but different presets
- the same drum kit, but different patterns?

any advice/explanations greatly appreciated.