TAB autocomplete for MutableNamedTuples works for first level only

Consider the following nested tuple example:
a = (b=(c=1,),)
In REPL I can type a. + TAB and I will see the level(s) below it. This can continue regadless of the number of levels in the tuple.

This only works for the first level if using MutableNamedTuples. I can discover only b, but trying a.b. + TAB yields nothing:
using MutableNamedTuples
MNT = MutableNamedTuple
a = MNT(b=MNT(c=1))

Did anyone encounter similar problems with autocompletion?
Is this a bug of MutableNamedTuples or Base?

This is a problem with tab completion that is fixed in 1.10 (REPLCompletions: replace `get_type` by the proper inference by aviatesk · Pull Request #49206 · JuliaLang/julia · GitHub).