When I open a standard size rc10 terminal from winbox 2.2.11, and then I maximise it (using 1280*1024 screen resolution) prompt line gets faulty and has strange behaviour. Prompt doesn’t update its position, as you can see in the attached image.
When I close this terminal, and open a new one, terminal size is stored, so the new terminal has this size, and it works correctly at this huge terminal size. It can be resized and maximised without problems.

rc11(demo2.mt.lv) winbox terminal is buggy too
i have this same problem… it seems that it’s trying to remember sizes and wrap around chars and its not getting it right.
confirmed on rc9 too…
I have the same problem with PuTTY on v3.0rc10 connecting to it through telnet and SSH.
thanks for the report, we are now working on it.