If you are viewing in a one-line space, as is usually the case, hitting the
enter key will put into a new line, thus making it appear to be invisible.
Hitting it more times will insert more blank lines making it more invisible.
Try hitting Shift-F2 (or arrow down) to see all of the contents it to see if
this is the case.

If you have truly confirmed that it is truncating to exactly 255, then the
above would not be an explanation.