Error when hovering over vertical scroll bar with more than one instance on page

Hi,

I've found that if I have multiple instances of the editor on a page, hovering over the vertical scroll bar of whichever instance is in focus causes an error. (attached screenshot)

I think the version is 4.2.1, though I'm not certain as I didn't download or install, I'm just working on it. The last version in the CHANGES file, is 4.2.1

regards,

Michael Lewis.