Looks like jq pipe ignores commas and parenthesis

I'm trying to understand the behavior of jq pipes when using parentheses and commas. Let's consider this JSON example:

{"menu": [    {"id": "file","value": "File","menuitem": [        {"value": "New","onclick": "CreateNewDoc()"        },        {"value": "Close","onclick": "CloseDoc()"        }      ]    },    {"id": "photo","value": "Photo","menuitem": [        {"value": "New","onclick": "CreateNewDoc()"        },        {"value": "Open","onclick": "OpenDoc()"        }      ]    }  ]}

First, let's apply a simple filter:

jq '.menu[].menuitem[] | .value'

Output:

"New""Close""New""Open"

This output is as expected.

Now, let's add a compound filter separated by a comma and group the first filter using parentheses:

jq '(.menu[].menuitem[] | .value), . | {}'

Output:

{}{}{}{}{}

It looks like second pipe is working with output of first filters

Question: why?

According to the jq documentation:

If two filters are separated by a comma, then the same input will be fed into both and the two filters' output value streams will be concatenated in order: first, all of the outputs produced by the left expression, and then all of the outputs produced by the right.

Following this logic, I would expect the output to be:

"New"    // output of first filter"Close""New""Open"{}       // output of second filter

However, this is not the case.

Corrected Filter

The filter works as expected if we add parentheses to the second filter:

jq '(.menu[].menuitem[] | .value), (. | {})'

Output:

"New""Close""New""Open"{}

Main question

Why does the pipe (|) operator seemingly ignore the parentheses and comma in the first compound filter? What is the logic behind this behavior?