SVN r4095 has fixes for a few corner cases. For example, bebox shows two slots that have no options in the -listxml data, but they are not listed in -listslots, which confused the slot editor (wasn't expected). Another issue was related to finding the right parent slot where a new slot should be added to.
I also found a few more drivers that allow slot recursion, for example cpc464/exp or kc85_2/exp, so there's a greater number of test cases than just vic20/exp
. They all look good to me now.