Steps to reproduce:

• Generate any two problems
• Mark one of it as a symptom for another
• Resolve the cause problem
• The symptom problem remains in that state (it's not reverting back to a cause).

Result:

• By default (unless the "Show symptoms" checkbox is explicitly set in the filter), this problem does not appear on the problem screen.
• Even if this checkbox is set and the problem is visible, there is no indication of which problem was its cause (since the cause is already resolved).
• These events do not appear in the audit records (Report → Audit Log), meaning there is no visibility of who marked the problem as a "symptom" or which problem was marked as the "cause."

Expected: 

• After the cause problem is resolved - all it's symptom problems became a separate cause problems
• Changing the problem to symptom/cause logged in the Audit Log.