Photoshop :: Merge To HDR Pro Causes CS6 To Stop Working

Having a problem which is easy enough to replicate when using Merge to HDR Pro ... either directly from within CS6, from LR4 or from Bridge it is causing CS6 to stop working.
 
What happens is that if you are using Merge to HDR then switch to another application causing Merge to HDR to lose focus eventually it will not recover and the Cancel/OK buttons are greyed out and not available. It never recovers from there.
 
Typical symptoms where Merge to HDR stops working (and therefore CS6) are the following:

- Any sliders that had been adjusted prior to this happening are available to change, others are not;
  - Any sliders that are greyed out can still be returned to their default value by double-clicking on the slider.
 
Photoshop has to be 'killed' before it can be used again.These symptoms are repeatable in the 32 bit version of CS6, the more files that are merged the quicker it happens. For example if you start with the "Photorealistic" preset and have 3 files open (opended using Camera Raw, Canon 5D mkII CR2 files therefore ProPhoto RGB; 16 bit; 5616 by 3744 (21.0MP); 300ppi)  it happens withing a couple of times switching to other applications and back but with 9 files open it will happen faster.
 
And it also happens with AdobeRGB (8bit), ProPhotoRGB (8bit) and sRGB (8bit).Happens from both x64 and x32 systems. The environment is follows:
 
Adobe Photoshop Version: 13.0 (13.0 20120315.r.428 2012/03/15:21:00:00) x64
Operating System: Windows 7 64-bit, Version: 6.1 Service Pack 1
System architecture: Intel CPU Family:6, Model:10, Stepping:7 with MMX, SSE Integer, SSE FP, SSE2, SSE3, SSE4.1, SSE4.2, HyperThreading
Physical processor count: 4
Logical processor count: 8
Processor speed: 2195 MHz
Built-in memory: 8173 MB
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