The paint bucket tool

The paint tool is starting to annoy me as I have encountered many problems with this tool.One problem is that the fill tool occasionally just doesn’t fill the drawing i am trying to colour even though there is no gaps whatsoever in the drawing. Why does it do this? Is there any way around this?
Another problem with the tool is that when i change the colour using the eye drop tool the paint tool still fills shapes using the previous colour. Again is there anyway to avoid this happening?