When writing a long message in a scroll, it is truncated to 250 characters or somewhat less, with no warning. It should at least warn about the truncation, or perhaps automatically wrap, if it can't just be allowed to handle a longer length.
There might just be a limit in issuing commands over a certain length, I don't know.
This is a problem specific to the GTKv2 client. It uses an old version of SockList which uses a fixed-length buffer of size MAX_BUF, which is 256.
One "easy" fix might just be to increase MAX_BUF to something bigger. The darkback is that MAX_BUF is used in a bunch of different places and it would be hard to check.
(In other words, other commands, including chat, shout, etc. with long arguments, are also affected.)