I think all the boolean modifiers used by this addon should explicitly set the solver to "CARVE". The default "BMESH" solver in Blender 2.78a breaks Line Rebools that are entirely enclosed by the target mesh and in other cases. BMesh doesn't seem like it should be the default, either, if Blender documentation is correct. Here's a patch for my update.

I think that the solver should be the option in the add-on preferences similar to Bool Tool.

Having an enum property gives more options for the user if one solver fails in certain cases.
If Carver works better with Carve then it could be the default option.

The patch doesn't set it to default but makes it the unique one.

That's simply the opposite side of the same coin. Blender's default is supposed to be Carve according to the documentation and there wouldn't be an issue with the booleans if that were still the case in 2.78a(I don't know when the solver default changed or if it is supposed to and the docs are just out of date). I would like to bring up that if you turn off Apply Operations in Carver MT, that patch would still allow you change the solver to address those certain cases. Perhaps both my patch and your suggestion are out of scope for this task.

However, I disagree that it should be a global add-on preference, that's too coarse a setting to deal with individual situations reasonably.

Blender default is BMesh solver since 2.78.

https://wiki.blender.org/index.php/Dev:Ref/Release_Notes/2.78/Modelling

They both have their own limitations.
BMesh fails with self intersecting and overlapping geometry.
For some tasks of the current ToDo's can the found here: T47030

Carve fails, for instance, in this case with non-closed geometry:

https://wiki.blender.org/index.php/Dev:Ref/Release_Notes/2.62/Boolean_Modifier

The option in the preferences can be set to be the default solver that can be toggled by a key for a specific
case - between it and the other option.

I don't agree that is too coarse, since carver is shortcuts only which are defined in the add-on preferences.

To get to any speed with the add-on they need to be learned.

Anyway, the default solver toggle maybe needs to be a separate task.

This task is getting messy but I don't see a way to reconcile this task with a new one if they were to be merged at the same time, so here's a new version of mesh_carver.py with all of my changes for this task and the preferences/key for changing the solver while using it.

hi, I think we are close to resolve here, will continue testing a few more days.

@Ted Milker (TedMilker)

Committed your patch with minor changes (mostly style and comments). Thanks :)
Works great.

Feel free if you have more patches to open new tasks.