[mrcz]

I cant move object to group in case of number of objects/groups ( lines in Object window) exceed some number which depends of resolution of display and icon size. See attached images. The number is 78 lines in my case ( small icons in the Object Window a 1600x1200 display resolution).
There is a workaround. I can rename the group temporally to a name which is similar to the name of the moved layer, sort alphabetically, move a rename back.