Yep, backend switching still also has a lot to be desired. Same thing for batch downloading tiles in the minimal network use mode - the "Loading..." place holder tiles will remain in the tile display cache and the newly downloaded tiles won't show up until the "Loading..." tiles are either evicted from the cache or modRana is restarted.

I plan to fix this soon, most probably by flushing the display cache after switching backends & once batch tile download finishes.