Wrong fixed headers when table is in bootstrap collapse collapsed

m.ardito

In this example https://jsfiddle.net/4aLmbgwg/8/

there are two examples, it's the same structure repeated twice, a datatables tale with scrollY put into a boostrap "collapse" panel.
each has its button to hide/show, but the first is generated already in the "open" state while the second is generated "closed"

but the first behaves well even closing and reopening it, while the second, after "opening" has headers completely wrong...

apart that, also columns widths seem to work well only in the first... anyway they are different in both cases...

Can anyone shade some light, explain how to fix this?

Thanks, Marco