Variable {customfieldvaluebefore} doesn't populate previous data if automation trigger includes card filter

Issue Summary

If you have a Custom Field related automation trigger with a card filter applied (i.e. "when custom field X is set on a card with the Y label), the {customfieldvaluebefore} variable won't populate the field's previous value.

Steps to Reproduce

1. Create sample automation: "when custom field X is set on a card with the Y label, post comment "{customfieldvaluebefore} has changed to {customfieldvalue}" 
2. Trigger the automation
3. Notice the comment is "has changed to [new value]", rather than "'[previous value] has changed to [new value]"

Expected Results

The comment should reflect the Custom Field's previous value and new value.

Actual Results

The comment only displays the new value.

Workaround

Currently there is no known workaround for this behavior. A workaround will be added here when available