Word spacing goes wrong on iOS Safari

[GoOz]

I'v been using the word-spacing property with a negative value on the text with bigtext on it.
While it seems fine on desktop (even with an iphone-like narrow viewport), on my iphone something went wrong.
If the value is positive, the text ends truncated.
If the value is negative, it fits but a horizontal scrollbar appears (most-likely because it thinks that the available space is the one without the negative word spacing).

Apparently, Safari doesn't support Subpixel font scaling, do you think that it's the cause of the bug? If so, is there any known fix for that?