Problems soft proofing on external monitor, unless moving image window back and forth

Problems soft proofing on external monitor!

I have encountered what I believe can only be a bug in Photoshop CC 2014:

My setup i a MacBook Pro retina, with an external Dell u2711 connected through display port. The monitors are calibrated with a custom profile, but the same behavior is present when using the default profiles for both internal and external monitor.

The problem is that sooft proofing on the external monitor gives very inaccurate results – unless I have first moved the image to the macbook internal display, activated and deactivated the sooft proof there, and then moved the image back to the external displays, after which it works as expected.

It is af Photoshop is unaware of it beeing displayed on a second monitor when activating sooft proof, but that the act of moving the image window back and forth causes photoshop to re-read the profile information and then display it correctly (which of course shouldn't be necessary.

There is a thread with someone experiencing a similar problem, but no solution

https://forums.adobe.com/thread/996694