"Show index tab for this language" becomes unchecked

After I “Update from Other source”, (9.3) the “show index tab for this language” box becomes unchecked. Checking these boxes again, and saving works fine. But, upon compiling the app, the boxes are unchecked again. The end result is that none of the (reverse) language tabs are showing. The workaround is to create a new app from scratch, but is quite cumbersome.
Any ideas or tips how to prevent this problem ?