This appears to be fixed in 1.13.0.18 beta
This also occurs in 1.13.0.18
I'm seeing this in 1.13.0.17 as well.
In 1.13.0.16, the code example for "executeCommand" is still incorrect.
Edit: executeCommand still has an incorrect code example in 1.14.0.1 Beta.
I attached file minecraft_addon_example_blocks_items_v1.1.0_only_packs.zip that contains block examples that worked in version 1.12.0.4. This example no longer works in v1.12.0.6.
I also tested in 1.12.0.4 and see the same behavior.
This still occurs in 1.14.0.1 Beta.