when activating auto normalize all brushes work as the add brush. is it normal?

Hi ddough__run ,

as far as I understand it, Normalizing Weights means that all Vertices that are assigned to deforming Bones, have a total Weight of 1.

If a Vertex belongs to only 1 deforming Bone, then it gets a weight of 1, when Normalized. 

So it's not so much, that each Brush is working as the Add Brush, but each Vertex is set to 1, in the Example with Suzanne.

If a Vertex belongs to 2 deforming Bones and both have a Weight of 0.5, than you can add or subtract something from either, subtracting 0.3 from one, will add 0.3 to the other.

Oh I think I know what you are experiencing - but I just wanted you to click on the ear so I could see the weights (if any) of the other group.

2 things can cause this.

This looks like you've been painting without auto-normalise enabled - which means the colours you see might not represent the true evaluated weights.   They are out of sync with each other.

Imagine 1 vert.  It is a member of 2 groups.  

Group A is set to 0.5 and Group B is set to 0.0
This will display as Green for A but in reality the colour should be Red (1.0)  

If you then  enable auto-normalise and paint on this vert (say you subtract 0.1), Blender will normalise the weights to 0.9 and 0.1
Technically you subtracted weight but the colour display went from Green to almost Red, which look like it increased in weight.

It did not - it just updated the view with the normalised weights.

Funky things can also happen when you auto-normalise a vert that is not a member of any deform groups. Blender will add it to the bone in question (and normalise it to 1.0 in that same operation), but then if it is only a member of that one group - it will stay at 1.0 because there is no other groups for it to auto-normalise with.

Hope that isn't too confusing, but try not to add a vert to a group with auto-normalise enabled.

Just looking at your video again now - I think it's the second thing that is happening to you.