PROBLEM
In weight paint mode selecting linked faces always only selects the UV Island by default.
If there is a way to change this behaviour I have not yet found it because link selecting does not bring up a selection type property box like it does in edit mode.
To select the whole part of the mesh the user has to have ‘face mode’ active in weight paint, then switch over to edit mode, select the whole mesh portion there and tab back to weight painting.
SOLUTION
Have an options box for selection type pop up in weight paint mode just like in edit mode.
I thought about proposing an option toggle in the n-key menue but I think having it behave just like in edit mode would be much more consistent.