The maximum size of a %postname% (or Post Slug?)

I wonder what is the maximum size of the %postname% (or Post Slug, wich is correct?) field?
I’ve got a post wich have a subject of 42 symbols wich should be translated into the %xy notation in order to be process correct by the browser, but it translate to the fewer post slug.
Here is the subject: “??????????? ??2?? ??2?????€??μ??????????? ?????????????????????????μ?€??°. ???????????€????o???????.”
Here is the Post slug generated: “%d0%b5%d1%81%d0%bb%d0%b8-%d0%b2%d1%8b-%d0%b2%d1%81%d1%82%d1%80%d0%b5%d1%82%d0%b8%d0%bb%d0%b8-%d0%bc%d0%b8%d0%bb%d0%b8%d1%86%d0%b8%d0%be%d0%bd%d0%b5%d1%80%d0%b0-%d0%b8%d0%bd%d1%81%d1%82%d1%80%d1%83%d0%”
As you can see the post slug just interrupted by ‘%’. I suppose it’s a bug or smth.
WP 1.3-a4, from the 6th of October downloaded from nightles directory.
PS. Sorry for bad english… :/