It seems it is currently not possible to add new statements with the `math` datatype. Because of some still unknown error, the js frontend is using `{"value":"a + b","type":"unknown"}` in its requests, both for `wbformatvalue` and `wbsetclaim`.
This //might// have started with `-wmf.11`, but it could also be that this is when T266493 started to happen.
Editing the value (in the existing statement) is not possible as well.
Reproducing the issue: edit https://test.wikidata.org/wiki/Q516#P717 and try to save the changed value. Observe the error preventing saving of the new value.
Notes:
* For local reproduction Math extension needs to be installed/enabled
* It has been speculated the issue might have been related to some broken "wiring" of data types
**Acceptance criteria**
* [ ] it is possible to add statements with the math data type again