It seems like breaking sunflower with a pickaxe enchanted with fortune (in my case, fortune 3) drops multiple sunflowers. I have not tested this with other tools or other flowers, though.

I think it's important to note that I had enchanted the pickaxe through commands (it also had unbreakable 3, mending and efficiency 5), and that I found this out while under the effect of haste 50 (yes, haste 50), also through commands. I drank a bucket of milk and the duplication still happened.

I tried again later with a pickaxe enchanted by hand and was still happening.

I couldn't attach a video of it happening because the file size limit is 10 MB.