When Adobe released their new, brilliant masking features in Lr & Ps > ACR, a new sidecar file came with it. If your workflow is like mine and your go from Photo Mechanic to Ps (Cmd / Ctrl +E) then you might see an ACR file appear on your lightable (only if you made a Mask in ACR). And if you Move your photos from your current folder in the lightable to a new folder, you might see that ACR sidecar file is left behind. Not to worry, the smart folks at Photo Mechanic have us covered!
To make the ACR sidecar not appear on your lightable, simply click View and uncheck Unknown Files as Proxies. And to move those ACR sidecar files with the rest of your files, go to Preferences > Manage file associations: > Edit and check ACR on the list! There ya go, you’re all up to day now.