I know there is at least one resolved bug at play here: [Bug-5869] Popup Resize Broken in 8.1.16 - #4 by cmallonee
I suspect that adopting a version which resolves that bug will fix both of your problems, because the horizontal scrollbar is likely due to the table not getting the space it expects to have available. I tried to replicate your issue in 8.1.19 with the following setup but was unable to:
- Table in Flex container, with table set to grow (
1). - columns with a width of 200px (and fixed at that width).
- View containing Table opened in Popup (no dimensions defined for Popup).