Steps to reproduce:

• Create HOST with two items:
  trap with type: log
  calculated item with formula: logsource(trap,pattern)
• (Or import attached XML zbx_export_hosts(8).xml)
• run server and sent to trapper value: "test"
• go to Latest data and observe that:

Result:
Calculated item became unsupported with error:

 Cannot evaluate expression: "Cannot evaluate function "logsource(pattern)": invalid regular expression.". 

Expected:
Calculated item should not match pattern and return 0