The scenario is very common, as in MS Word the option Table -> Layout -> Cell Size -> AutoFit ->  "AutoFit Contents" changes the PreferredWidth of the table and its columns to Auto.
Also the tables imported from HTML have these properties set by default.

Scenarios:
- Auto-sized table occupies minimal space.
- All auto-sized columns in a table (table itself could be, or could be not, auto-sized) should always be sized proportionally to their content length. Currently, such columns are sized equally in the case when there is enough space for all of the content, which is unexpected. (also see the attached images for the scenario with fixed-width table + auto-sized columns).