pingback url is right-trimmed incorrectly

[qdinar]

an url ending with %d0%b5%d1%81% was produced by pingback mechanism, that url is in pingback comment, and server returns for its request:
Bad Request
Your browser sent a request that this server could not understand.


but if it would end with %d1%81 it works. wordpress automatically fixes it. but also it does not open if it ends with %d1%8 or %d1 .