Conditions by default do not function in backend. You can enable this in CB Conditional > Parameters, but I strongly suggest you don't as it makes management of users a bit of a nightmare with fields conditioning away. Value resetting should also be enabled by default within CB Conditional > Parameters as is responsible for resetting the fields value when the condition fails. If it's turned off the value won't reset.
It doesn't particularly matter if the database value isn't emptied as on HTML view CB Conditional will empty the field anyway. CB Conditional doesn't touch the saving process of a field; there's too much risk in breaking a fields save capability. The reason for this is how a field handles being empty is widely different on a field by field basis. At any rate will look into it further for a later release.
forge.joomlapolis.com/issues/5233