Structural Rules

I am using OpenBuildings Designer CE update 5 (, but I have also confirmed the below problem in the latest version.

When applying structural rules to plan views I always have Delta TOS set as one of the attributes all the applied rules.

I  also ensure that when DTOS equals 0 that it is set to "Hide labels when delta = 0" in the view presentation options.

I am finding that this is not working as shown in the plan below:

It can be seen that there are a couple of variations in the DTOS display - one with brackets and one without.

I tried both options when setting up the rules but neither vanishes.

I should not see any form of DTOS where 0 appears.

Is this a bug?