Report Builder bar graph does not show any results while drill down into Unassigned state of TCER

In Report builder, when we build a report for Test execution status, the Unassigned TCERs does not display any results when we drill down from the bar chart.

Steps to reproduce this issue:

Open Report Builder v6.0.3 (I guess this issue is there in earlier versions aswell)

In "Choose Data" tab, configure the below.
Report Type : Current Data
Choose an Artifact : Test Plan
Teace Artifact Relationships : Test Plan --> Test Case --> TCER
Set Conditions :
TP ID is xxxx
(TCER) Test Plan Name is yyyyyy

In "Format Results" tab, configure the below
Under 'Format', choose 'Table' and click on 'Add Calculated Value Columns' and then select TCER from the drop down of 'Attributes of :'
Then under 'Choose a calculation', select 'Count number of Artifacts'. Under 'Choose All or Limit', select 'Limit (....)'. Under 'Choose an Attribute', select 'Current Result Verdict'. Under 'Choose Limiter values' select 'Unassigned'
Click Add and Close

Now, under 'Format', switch the tab to 'Graph'
For x-axis, choose 'Test Plan'
For Y-axis, select the radio button 'Add lines or bar segments from numeric measures' and then select the newly added calculated value. If that won't appear, click on refresh (which is found next to Graph tab)

This will list all the TCERs which are in 'Unassigned' state in the test plan.

Now, run the report by going to the final tab which is ''Run Report''

Here, if we click on the bar chart to drill down, it will show no results.
But the bar graph is showing results (drill down will not show results)