I have noticed a regression in behaviour in relation to theme symbols, and I am not entirely sure what is causing it: I had managed to get the new lock theme symbol for all the themes working on the debug build yesterday, but this seems to have stopped working to-day. It still seems to work with the flat theme, but no others. I am having trouble working out what has changed since yesterday - can I check whether I have merged the themes properly or whether my build script is pointing to the correct files? I am using the files in themes.src.
The state of the themes.src folder on your master branch is definitely up to date.
The packages and themes downloaded from http://bridgewater-brunel.me.uk/downloads/nightly/packages/ are also up to date and the lock symbol is displayed.
But what exists in simutrans/themes on master branch remains old. I suspect you used it.