The -1 thingy is actually a new feature, proposed by Jinx. (thx Jinx)
The old wechall did not store your solved challcount, only scores ... the new code will also store solved challcount, but the data has to be generated first.
As soon as you update a site and it produces some change, the challcount will be updated as well. Either -1 (not supported for this site) or the hopefully correct value.
I will check all site updates soon, so stay tuned ;)
... Sadly i have no list of new features in WC5 ...