Text engines change from version to version, and as soon as you touch a text frame it is going to recompose the entire story. You should, as a matter of course, expect text reflow and other similar changes (like problems in tables) whenever you update a document to a new version.
I prefer to export legacy files to .inx or .idml from the original versions and convert that. This is anecdotally less likely to have problems down the road, and it will force a complete document recompose, getting the surprises out of the way early.
export legacy files to .inx or .idml from the original versions and convert that
I tried that and was able to import a copy with the same corruption problem.
Just found a fix (Yay!)
1. Do not change anything in the bad table. This way it will still be visible. You can move it though.
2. Note how many rows and columns in the bad table (Shift F9 to see the table window)
3. Create a new text box of the same size and assign the content as text.
4. Select the Type tool and from the menu select Table>Insert Table
5. Create the same number of rows and columns as the bad table. I found I had to do this step
6. Select the content of the bad table from the upper left corner (angled arrow)
7. Highlight the entire new table and paste your content into the new table.
8. The new table should be back to normal.