oops, sorry for the last post, the command-line rebuild of the Xapian cache restores also the search button - I had the target still set to "version" from previous trials. So, summarizing: after upgrade from LTS to LTS the Xapian cache is outdated, and Synaptic doesn't recognize this and so misses a rebuild.
oops, sorry for the last post, the command-line rebuild of the Xapian cache restores also the search button - I had the target still set to "version" from previous trials. So, summarizing: after upgrade from LTS to LTS the Xapian cache is outdated, and Synaptic doesn't recognize this and so misses a rebuild.