VSCode extension yaml auto-complete not working in vscode 1.43.1 and yaml extension 0.7.2

I am testing vscode 1.43.1 example from here and have some issues.
When I set registerCompletionItemProvider language option to "yaml", the auto complete item results not showing anymore until I uninstall the yaml extension.
It worked on vscode 1.42.1 with yaml extension. Does anybody encounter the same issue?

I also ask this problem in vscode github:
https://github.com/microsoft/vscode/issues/93279#issue-586666956

• VSCode Version: 1.43.1
• OS Version: Mac os mojave 10.14.5
• YAML Extension Version: 0.7.2

Steps to Reproduce:

1. Install YAML extension.
2. Using vscode-extension-sample: completions. The trigger character is ., and I modify the language from plaintext to yaml.
3. Run it and open an empty yaml file, then keying console..

Input console. in the empty yaml file. There has no item to show.

When I disable YAML extension, it seems work.

Start with completions-sample/src/extension.ts around line 49 and reproduce the behavior using VS Code 1.43.1, the YAML extension 0.7.2, and an empty YAML file. Compare completion behavior with the YAML extension enabled and disabled; done means the sample's completion items appear while the YAML extension remains enabled.