I've found that static zimlet files (js/css) are cached by the server.
Server restart helps but it is too awkward solution for me as I have to develop on slow server and the operation takes too much time.
"?dev=1" also helps but it brings in another slowness because JS files are transferred uncompressed and I have unstable 3G connection.
I'm searching for something like "zmmailboxdctl flushcache".
Is there anything better than two solutions I mentioned above?