Wow, this is crazy!!!
It works fine with $1, $2,..., i.e. you can use them in gui properties at the end, beginning, middle, wherever you want and doing it with the properties editor - the only weirdness is that when you re-open the properties dialog the $ will be replaced by a #, but everything works fine. I've been doing this for years (since 0.40 you can put them in the middle and use multiple dollars in a symbol, at least as object creation arguments).
However, the $0 is not handled properly. It is immediately "interpreted" and becomes a 0, as Ben described.
I use $n's a lot, both as object creation arguments and as gui object properties, and not only as prefix, but I never noticed this because I usually don't use $0 in gui properties and whenever I use $0 it is usually as a prefix...
This is definitely a bug: there's no reason why $0 should be treated differently than $n with n>0.