The new UI doesn't show stacked graphs properly when series go on and off

[simonpasquier]

What did you do?

Running Prometheus with 3 targets: prometheus, alertmanager and node-exporter.
Initially only prometheus and alertmanager are up, then node-exporter comes up, then alertmanager goes down. Eventually alertmanager comes up again.

After that I've queried process_virtual_memory_bytes with the stacked graph in the new UI.

What did you expect to see?

Properly stacked graphs.

What did you see instead? Under which circumstances?

Environment

• Prometheus version:

7a541bd

• Prometheus configuration file:

scrape_configs:
- job_name: 'prometheus'
  static_configs:
    - targets: ['localhost:9090']
- job_name: 'node'
  static_configs:
    - targets: ['localhost:9100']
- job_name: 'alertmanager'
  static_configs:
    - targets: ['localhost:9093']

[roidelapluie]

Thanks! ccing @juliusv

[roidelapluie]

Reproducer: https://prometheus.demo.do.prometheus.io/new/graph?g0.expr=vector(1)%20or%20label_replace(vector(1)%20%20and%20(vector(time())%20%25600%20%3C%20300%20%20)%2C%22x%22%2C%221%22%2C%22%22%2C%22%22)%20or%20%20label_replace(vector(1)%2C%22x%22%2C%223%22%2C%22%22%2C%22%22)&g0.tab=0&g0.stacked=1&g0.range_input=1h&g0.end_input=2020-07-11%2009%3A30%3A00&g0.moment_input=2020-07-11%2009%3A30%3A00