You have to provide the following information whenever possible.

**Describe the bug**
This query fails with the latest stable version 21.5.5.12. It worked with the last stable version 21.4.7.3.

**Does it reproduce on recent release?**
yes

**How to reproduce**
21.5.5.12

```
SELECT
    label,
    number
FROM
(
    SELECT
        'a' AS label,
        number
    FROM
    (
        SELECT number
        FROM numbers(10)
    )
    UNION ALL
    SELECT
        'b' AS label,
        number
    FROM
    (
        SELECT number
        FROM numbers(10)
    )
)
WHERE number IN
(
    SELECT number
    FROM numbers(5)
)
```

**Expected behavior**
Query should run without errors

**Error message and/or stacktrace**
```
Received exception from server (version 21.5.5):
Code: 49. DB::Exception: Received from localhost:9000. DB::Exception: Block structure mismatch in Pipe::unitePipes stream: different names of columns:
label String String(size = 0), number UInt64 UInt64(size = 0), 'b' String Const(size = 0, String(size = 1))
label String String(size = 0), number UInt64 UInt64(size = 0), 'a' String Const(size = 0, String(size = 1)).
```

{
    std::unordered_map<const Node *, ColumnWithTypeAndName> node_to_column;
    std::set<size_t> pos_to_remove;
    {
        std::unordered_map<std::string_view, std::list<size_t>> input_positions;
        for (size_t pos = 0; pos < inputs.size(); ++pos)
            input_positions[inputs[pos]->result_name].emplace_back(pos);
        for (size_t pos = 0; pos < header.columns(); ++pos)
        {
            const auto & col = header.getByPosition(pos);
            auto it = input_positions.find(col.name);
            if (it != input_positions.end() && !it->second.empty())
            {
                auto & list = it->second;
                pos_to_remove.insert(pos);
                node_to_column[inputs[list.front()]] = std::move(col);
                list.pop_front();
            }
        }
    }
    ColumnsWithTypeAndName result_columns;
    result_columns.reserve(index.size());
    struct Frame
    {
        const Node * node = nullptr;
        size_t next_child = 0;
    };
    {