[Freesurfer] tkmedit white matter editing

Dear all I am using the tkmedit GUI to add/erase pixel in a slice-wise fashion in order to subsequently apply a tessellation on the white matter. I launch the command

cd subject/mri tkmedit -f brain.mgz -aux wm.mgz

from linux shell (64bit CentOS), where brain.mgz is the anatomical MRI and wm is the segmented white matter, both in the subject/mri folder Editing the voxels of the aux image works only when i want to insert pixels but not when i want to erase them (menu->EditVoxelsTool->right mouse click). I wonder if anybody uses this feature of tkmedit GUI and had the same problem.

Appreciate any input Best, Cristiano