I cant add some parts to containers in VAB. Others can be added. Nothing (no "part too heavy") is displayed.
Can add: Modular Gilder segment, basic ladder.
Can't add: Tools (screwdriver, wrench), engines, fuel tanks, most other parts.
Using KSP 1.8 (KIS is for 1.7... is it the root cause?)
Thanks!
EDIT: I can see there are problems with KIS and KSP 1.8. So it is probably root cause.