Pasting CMS Collections into tabs

I can’t seem to paste a CMS collection into different panes of a tab element. I used to be able to do it, so I am wondering what’s changed?

I can paste into one pane, but when I try to paste into another the error message reads:

“You cannot have more than 1 nested collection page on a single page.”

Has anyone else noticed this? Does anyone know a workaround?