See https://www.reddit.com/r/feedthebeast/comments/6a881q/ftb_beyond_unofficial_changelog_for_the_v160/dhhzq78/?context=5 for original report.

Fixed by PR #946

Summary: The Modify Weed Spawning Mechanics commit introduced a typo replacing the less-than with a greater-than inequality. As a result, an Aggressive plant with Strength lower than a neighboring plant would always spread and replace the other plant.

Nice detective work! I tip my hat to you sir.

Thank you! :)