When two channel identifiers have the beginning of their identifier which is equal, and that beginning is equal or greater than 63 characters, this results in a "Duplicate definition" error at syntax checking.
For example, if you open a brand new UPPAAL modeling, put the following lines in the declaration section, you obtain a "duplicate definition" error.
urgent chan ttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttt1;
urgent chan ttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttt2;
I've seen no such restrictions mentioned in the grammar, but I may have missed that information.
By the way, I found this bug because I have written a UML-to-UPPAAL automatic code generator which may generate long channel names.
Your observation is correct. I can either take this as a documentation bug or as a request for enhancement - your choice :-)
Well, actually, there is at least one bug: UPPAAL should not provide an "duplicate definition" error, but rather a "invalid identifier" error, even if the documentation is updated.
But you may consider this as a request for enhancement!