Toggling "show hidden files" only affects the right pane. Giving focus to the left pane makes no difference, after showing hidden files, it switches focus automatically to the right, and then toggles that pane. Fresh install, default settings. I see no option to change this behavior Krusader 2.5.0 KDE 5.8.2 Frameworks 5.27.0
For whatever reason, the next time I opened Krusader, it stopped doing this. When this was happening, it was after a fresh install and during the first run.
Will close this for now. Please reopen if you can confirm it again.