Tags (Categories) completely broken in 4.7.20 on Ubuntu 16.04 LTS

I've just clean installed CiviCRM 4.7.20 on Ubuntu 16.04 LTS (with latest WordPress, but I think that's irrelevant) and tags seem to be completely broken. If I click the Tags (Categories) item in the Configuration Checklist I just get an error message "Sorry but we are not able to provide this at the moment". Looking at the error log (extract below), it's pretty obvious this is a well-known problem due to the change of the default "sql_mode=only_full_group_by" setting last year in MySQL. The workaround is to change that setting, but it's there to prevent non-deterministic behaviour and I'd rather not impose that on all my sites.

I couldn't find an existing bug report for this, but as I say it's a well-known problem so if it's a duplicate I apologise. I don't use tags as it happens but anyone who does will probably regard this as a major bug when they upgrade. Ubuntu is a pretty popular OS and earlier LTS versions run unsupported PHP versions so I'd say this is fairly urgent.

Jun 14 00:52:27 [info] $Fatal Error Details = Array
(
[callback] => Array
(
[0] => CRM_Core_Error
[1] => handle
)

[code] => -1
[message] => DB Error: unknown error
[mode] => 16
[debug_info] => SELECT tag.*, child.id AS child, COUNT(et.id) as usages
FROM civicrm_tag tag
LEFT JOIN civicrm_entity_tag et ON et.tag_id = tag.id
LEFT JOIN civicrm_tag child ON child.parent_id = tag.id
WHERE tag.is_tagset <> 1 AND tag.parent_id IS NULL
GROUP BY tag.id
ORDER BY tag.name nativecode=1055 ** Expression #12 of SELECT list is not in GROUP BY clause and contains nonaggregated column 'beechesit.child.id' which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by
[type] => DB_Error
[user_info] => SELECT tag.*, child.id AS child, COUNT(et.id) as usages
FROM civicrm_tag tag
LEFT JOIN civicrm_entity_tag et ON et.tag_id = tag.id
LEFT JOIN civicrm_tag child ON child.parent_id = tag.id
WHERE tag.is_tagset <> 1 AND tag.parent_id IS NULL
GROUP BY tag.id
ORDER BY tag.name nativecode=1055 ** Expression #12 of SELECT list is not in GROUP BY clause and contains nonaggregated column 'beechesit.child.id' which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by
[to_string] => [db_error: message="DB Error: unknown error" code=-1 mode=callback callback=CRM_Core_Error::handle prefix="" info="SELECT tag.*, child.id AS child, COUNT(et.id) as usages
FROM civicrm_tag tag
LEFT JOIN civicrm_entity_tag et ON et.tag_id = tag.id
LEFT JOIN civicrm_tag child ON child.parent_id = tag.id
WHERE tag.is_tagset <> 1 AND tag.parent_id IS NULL
GROUP BY tag.id
ORDER BY tag.name nativecode=1055 ** Expression #12 of SELECT list is not in GROUP BY clause and contains nonaggregated column 'beechesit.child.id' which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by"]
)