when a correct xcursor theme is set via the environment it is correctly used for all clickable items (user, password field, login button etc.). however for everything else the cursor is the default x X cursor (the one that is an actual X). This is inconsistent and ugly, supposedly the theme needs to explicitly set a cursor everywhere to prevent this sort of behavior.

Alternatively according to startkde the following should switch the default cursor to the left_ptr type (or that's what I read out of it anyway):
xsetroot -cursor_name left_ptr

Reproducible: Always