I find it very annoying that you can grab containers (which I do by accident while working in 0-g due to the gui moving around) but not attach them.

I would far prefer not being able to pick them up at all to the current state, but probably the best would be to make them attachable as well.

The container mounting brackets allow you to place containers back on vessels. Are you mounting containers directly on other parts?

I was trying to, yes. I did not see the container mounting brackets during construction and they are not mentioned in the forum post or wiki. It never occurred to me that such a thing would even be needed. Now that I know, I'll start using them!