Extra processing when switching to another disposition

[fedelin]

Hello all,
XnView MP / Linux Mint 18.2 / Cinnamon
I have customized 2x dispositions and XnView is pointing to a 6500 photos library.

Each time I switch the disposition (let say) from A to B, XnView is starting a process with a percentage bar at the bottom of the screen. It takes 2-3 minutes to reach 100%. Once done, if I switch to another disposition, it does start again.
What is is doing? How can I avoid this extra process?

Thanks for your help
François

[xnview]

you means a 'custom layout'?