Surprisingly could not find this in a search -
At the moment its happening when I open a photo from Lightroom to edit in Photoshop. If I have one open and launch another from Lightroom it opens a separate copy of Photoshop.
I can remember this also happening once when I opened a photo from finder after already having a photo open directly from photoshop.
MacPro [early 2009] 2 x 2.26 GHz Quad-Core Intel Xeon 32GB | OSX 10.8.5 | Photoshop CC 14.1.2 x64 [up to date as of 23/12/2013] | Lightroom 5.3
System Disc 1TB | Working Volume 1.5TB + Scratch Volume 1.5TB on 3 x 1TB RAID 0
Retrieving data ...