Large selections make GUI awfully slow

[lucmp]

After a long scan, I realized I should have excluded a certain directory. I looked for it in the list of changes before applying the changes. I selected all files aiming to exclude them, hundreds of them, and... the GUI froze for about half an hour. The 'top' command indicated the 'python' process taking up 100% of the CPU.

It became responsive again eventually so I applied the changes. It took a very long time, more than one hour. There were many changes to be made, but I have done this before and it never took so long.

After all the changes, that large selection of hundreds of files was still there. I clicked one item outside the selection, to clear the selection, and... the GUI has been frozen for about half an hour as I type this, and 'top' indicates the 'python' process taking up 100% of the CPU again.