Trigger in problem state hides all dependent triggers in history view

Steps to reproduce:
1. Create two triggers, make trigger 1 dependent on trigger 2
2. Create some problem, which activates trigger 1, and then trigger 2 after some time
3. Resolve the problem
Repeat steps 2 and 3 multiple times

Look in Monitoring - Problems, switch to History view
When trigger 2 is active, only trigger 2 problem history is shown, all history related to trigger 1 is hidden, even for previous problem periods
When trigger 2 is not active, all history for trigger 1 and trigger 2 is shown

Expected:
Historical problem data is always visible and do not depend on current trigger state - they are historical data !

Attched screenshots:
CPU LOAD HIGH depends on CPU LOAD VERY HIGH
when CPU LOAD VERY HIGH is in problem state, all history for CPU LOAD HIGH is hidden.