This was working before. This feature was broken twice in 3 years.
Please ensure for all editors and all browsers (e.g. Chrome) and for all applications (wiki,forum,blog...) that it is possible to copy/paste images directly from the clipboard (without having to store it to a file locally.
Ensure means also check after any update that this feature isn't broken again.
Currently with textbox.io 6CR5 it does not work in blog and wiki (seems to work in forums)