Online update from the application itself does not work, so doing an offline update seems the way to go. That also may not work because of file creation errors. In that case a possible solution is to create a new bottle, run the offline installer (it may be necessary to create 'drive_d' directory including its link in 'dosdevices' beforehand) and then copy all created files over the previously installed application in another bottle. An update check from within the application afterwards did not report an outdated state anymore so that procedure of updating seems to work.