So I’m trying this:
•I select a default DynaMesh32 sphere from Lightbox.
•I select the CurveTube Brush, turn of symmetry and ALT+click to draw out a Curve Tube. (This should tag the Curve as Negative/subtractive geo).
•I reposition the Curve Tube with Transpose, but keep it intersecting with the Sphere.
•Then I CTRL+ALT+LMB-drag on the canvas to trigger a clear mask+remesh in one go.
The result is an addition of the tube to the Sphere. Not the subtraction I expected.
If I do the same thing but leave out the Transpose step, the remeshing does occur with the tube being subtracted.
But it gets weirder…. If I use a DynaMesh16 sphere from Lightbox and do the same thing, subtraction does happen but the Sphere is subtracted from the Curve Tube instead of the other way around. Leaving off the Transpose does not change this erroneous behaviour in this case. Running the clear mask and remesh in two separate click+drag actions makes no difference.
When I use a DynaMesh64, everything works as I’d expect, including any Transpose movements thrown into the mix. Same with DynaMesh128, so it seems it’s just the two lowest resolution DynaMeshes that are causing anomalous behaviour. Remeshing those to a higher resolution does not solve this.
Very confused… Would love to know if anybody else is experiencing this. 
Running on OSX 10.6.7.