This is a usability issue and has been present following the recent major update and introduction of more extensive multi-tasking.
Simple case is when using Sync in the develop module.
After initiating the Sync I find that I can no longer step to the next image using the keyboard arrows.
It's irritating, my method of working is to Sync the changes then step through the undated images to check the changes are OK.
But I find that the user interface has lost control and sometimes the current image disappears.
Its necessary to click on a thumbnail to regain control focus. This woks but is a) time wasting and b) if the wrong point is clicked means you lose the images selection and have to waste even more time re-establishing the selection.
This looks to me like a coding issue, relating to how the user interface activates a background thread to perform the Sync but does not retain control focus.