If you have multiple triggers that set a value in a multiple select field they will overwrite each other.
For example if I have trigger 1 that sets value A to a field and trigger 2 that sets value B.
When trigger 1 runs it will set the value of the field to A.
If trigger 2 then runs subsequently it will set the value of the field to value B and effectively deselect B.
I would like the option for it to add the value for B and retain A as well.