Colour replacement tool not working like it used to

[roberts33286217]

I used to use the colour replacement brush and liked it but on more recent versions of Photoshop I'm not getting good results, whenever I drag the brush across the colour I wish to change I get streaks through the colour (see green area on attached pic). Have I changed a setting that I'm not aware of?

[roberts33286217]

Anyone else having the same problem?