As an editor, I want to be able to edit negative quantity amounts easily, in order to fix them if they’re wrong.
Wikibase uses the character − (U+2212 MINUS SIGN) to format negative quantities (instead of - U+002D HYPHEN-MINUS), but does not recognize this character when parsing quantities (at least in English). This means that after entering a negative quantity as e.g. “-10”, trying to edit it again presents it as “−10”, and changing it to e.g. “−100” doesn’t permit saving (the “publish” button is disabled) – you have to manually change the minus sign and save “-100”.
Can be tested easily enough on the sandbox item.
* Wikibase parses − as a negative sign for quantities.
* Are any other characters affected? Keeping in mind that quantity formatting is localized.