When you log into Roundcube, folders (and folders metadata) cache is cleared (all entries removed). The same is done in Chwala. I propose to not clear the cache in Chwala. Reasons:

1. Syncroton does not clear the cache (for technical reasons).
2. The main entry point to Chwala functionality is Roundcube, so there's no need to clear the cache twice.
3. Because just after Roundcube login we immediately connect to Chwala (since Kolab 16), this causes the cache entries already filled by Roundcube to be removed by Chwala, which causes slowdown (or possible cache inconsistency in case of memcache).