I'm not sure what you mean, or what you are doing.
The full load/no loading/force unload are modifiers for existing orders. You need to select one or more orders and then use those buttons to mark the loading/unloading rules for those selected orders. If this didn't work someone else would have reported it a year ago.

Sorry I was a bit cryptic. This is a subset of my hotkeys.cfg:

[order]
fullload = J
no_load = L

If inside any order I select the station and press J, it toggles between setting "Full load any cargo" or removing it.
But If I press L, it only sets the "No Loading" option, it never removes it.

Furthermore in the UI when selecting "Full Load any Cargo" or pressing key "J" it updates the options below.
But when selecting "No loading" or pressing "L" it doesn't update the options.

I'm using the Windows 64-bit version.

I'm not sure why @LC-Zorg's comment was marked as off-topic. I understand that it doesn't relate directly to the reported issue, but I have also experienced difficulties with explaining how this window works to newer players. A redesign (even if less major than what was suggested) might not be a bad idea to consider.