[Material hotend temp not changing]

The issue is still present in v5.1.1

 

I believe I found a solution. The issue comes from the default config for the respective filament.

 

For instance, in the following file:

c:\Program Files\Ultimaker Cura 5.1.1\share\cura\resources\quality\twotrees\pla\two_trees_0.4_PLA_standard.inst.cfg

 

you need to remove the values for the temperature (delete the following lines):

material_bed_temperature = 60
material_print_temperature_layer_0 = 195
material_print_temperature = 190

 

That solves the issue for PLA. 

You will need to do the same for the other filaments in the respective Printer/nozzle configuration, i.e. file.