Steps to reproduce:

1. Create a host
2. Create an Item with "HTTP agent" type
3. Create a Dependent item for the Item from step 2
4. Add a "Prometheus pattern" Preprocessing step with Parameter where label name and label value match only one metric (Example: {event="add",role="endpoints"})
5. Press Test action for the Preprocessing step
6. Add the Value from attached file prometheus_output.docx
7. Press Test action button
8. Observe, that found multiple metrics, even without label from step 4

Result:
Preprocessing step founds metrics which are not matching searching parameters. Please, see screenshot multiple_finds.png

Also related to the Prometheus to JSON preprocessing step.

Expected:
Preprocessing step returns metrics that match searching parameters only. (prometheus_sd_kubernetes_events_total metric in example)