System Information
Win 7, GTX 560ti
Win 8, GTX 980

Blender Version
Broken: 2.74 release
Worked: not sure

Short description of error
When float buffer on

1. Repaint an image with alpha locked, result in the semi transparent edges to glow

note: Alpha on/off as in the UI (not alpha lock ON/OFF)

2. With the same setting, if you select another hue for the repaint (alpha locked), glitch color will be produced

Exact steps for others to reproduce the error

Note: Please turn off Alpha lock (meaning tick alpha)

For alpha edge problem:

1. Paint with the brush,
2. turn on alpha lock,
3. repaint with the same color,
4. observe the edges

For the color glitch:

1. Paint with the brush,
2. turn on alpha lock,
3. repaint with another hue,
4. Glitch may appear, if not, try another color.

Thanks in advance.