filter[system:creation-date] not working

[cylkee]

Sym 2.7.10
PHP 7.3
OS Linux

API filter on system date not working same as back-end UI filter on system date

Steps to reproduce:

1. Navigate to a section with entries created this year (or date of your choice)
2. Use the back-end filter UI to filter on System Creation Date: is 2020 - expected entries returned
3. Repeat step 2 with is 2019 - expected entries returned
4. Copy the relevant URL parameter to apply it to the API URL, e.g. /symphony/api/entries/section-handle/?filter[system:creation-date]=2020 - all entries are returned unfiltered
5. Repeat step 4 with 2019 - all entries returned unfiltered

Other field filters appear to be working as expected.