The 30th of Winter. Huh, yeah that IS a weird glitch. Use it to your advantage then! Try with others - I only plant soybeans now and it hasn't happened to me. But I'm not looking for that so never noticed.
I had heard about this glitch and I tried to trigger it in my first file, and it didn't work for me...maybe I did something wrong, I don't know...or maybe it's somewhat random. Who knows? ^_^ But yeah, if you can get it to work, might as well take advantage of it! I have not heard anybody reporting a similar glitch with any other grains, though, so I'm fairly sure it only happens (sometimes) with wheat.
It happened to me on my first file. I also play the DS. But I didn't plant it on the 30th, it was on the 27 if I'm not wrong. Anyway, that happened. It seems to be kinda random, but I would say you're really lucky to get it to work 3 times already!