Re: Shrinking Violet Bug

It's mentioned on the wiki page and it's the same for Kernel-Pult, Iceberg Lettuce etc...so I'd guess it's intentional: https://plantsvszombies.fandom.com/wiki/Shrinking_Violet 

Zombies that have been stunned or frozen by Kernel-pult, Iceberg Lettuce, Stunion, or similar plants cannot be shrunk by Shrinking Violet. However, zombies that have been slowed down by plants such as Snow Pea, Winter Melon, Stallia, and similar plants can still be shrunk.