ID 312192 - Switching to and from Monitor tab while preview rendering causes lag

Problem summary
When preview rendering a scene in Katana, if the user decides to switch from the monitor tab to view another tab, the render will continue but it will cause quite a bit of lag when switching back to the monitor tab.

The loading lag becomes worse the longer the user takes before switching back to the monitor tab.
I have had Katana go into 'Not Responding' for a few seconds, this may cause some users to try and quit Katana before it finishes loading.

Steps to reproduce

1) Open the 'Hello Pony' example scene via 'Help -> Example projects'.

2) Below the 'PrmanGlobalStatements' node, create a 'RenderSettings' node and set the resolution to 4K (Or another large resolution size).

3) In the 'PrmanGlobalStatements' node, set the pixel variance to '0.001'.

4) Expand the Scene graph on the 'RenderSettings' node and 'Right click the RenderSettings node -> Preview Render' 

5) Once the render has started, switch the monitor tab to any other tab.

6)  After about 30 seconds, switch back to the Monitor tab.

Result)  When switching back to the Monitor tab, there will be a few seconds of unresponsiveness before the Monitor is loaded. 

Workaround

Try to keep the Monitor tab open while rendering.

If you do not want to view the tab, then wait till the render is complete before switching tabs.

Reproduced by support
Katana2.6v3 - CentOS6.9 - Windows 7
Katana2.6v1 - CentOS6.9 - Windows 7
Katana2.5v7 - CentOS6.9 - Windows 7
Katana2.5v1 - CentOS6.9 - Windows 7
Katana2.1v6 - CentOS6.9

Earliest version tested
Katana2.1v6

Expected behaviour
There should be no lag or unresponsiveness when switching tabs.

Actual behaviour
Switching to the Monitor tab while it is rendering causes lag and unresponsiveness