See https://github.com/minetest/minetest/pull/5115 for details.
You may have noticed that when using 'visual_scale = ' for a plantlike node the scale acts weird, turned out it was applied twice, squaring the value.
This is now fixed but means you need to adjust your scale value.
If you wanted a specific scale just use the value you wanted and it will now be correct.
Otherwise, just square the value you were using before to get the same result.
Sorry for the breakage but we are early in a release cycle so there is a few months to do this before next stable Minetest release. If you intend your mods to be used with Minetest 0.4.15dev then you will need to update immediately.