Can't layer samples in pads

Hi all!

I’ve upgraded to 11.0.10 and trying to layer samples in a single pad in GASE5 but the sample drag-and-drop dialog won’t cooperate beyond “Replace Sample” (can’t upload images or links yet, sorry!), i.e. when I drag a sample to an empty pad it works, but when I try to drag another sample to the same pad, only the middle option is highlighted, even when my mouse is hovering the sample over the “plus” option.

Any help would be appreciated!

Nevermind! I was trying to drag pre-made pads from the Groove Agent library instead of audio samples.