I couldn't find the inconsistency last night, but I think it's my mistake. The release version brush I was using didn't have Blend Transparency set to 'Full', so I thought there was an inconsistency.
When using Basic > Hard Static Round with same settings, the release version and Beta are consistent regarding Blend Transparency modes.
I didn't expect a Behind Blending mode to blend at all with existing strokes, but it makes sense that it does when set to 'Full'.
Edit: Forgot to mention in the first post that clear blending mode (temp) will not 'clear' paint when blend mode is set to full. It seems to ignore the Clear Blending (temp) mode and applies the current color if brush is set to 'Full'.
Setting a brush to 'Clear' Blend (not temp) mode does clear existing paint when Wetness > Blend transparency is set to 'Full'.
I'm setting the non temp blending modes from the tool options in the sidebar.
Steps to repeat:
Brush > Basic > Hard Static Round
Wetness > Blend Transparency to 'Full'
Blend Mode > Clear (temp) (I'm using quick menu for this)
Brush will paint with color, not erase. (Other blend Transparency modes will erase)