Mkdir creating packages, not folders [in Terminal]

Question

For a while now, I've been using this terminal command to create folders based on a list in a text file. It's worked well, including in Yosemite.
cat dirlist.txt | xargs mkdir
An example of the dirlist.txt file would be this:
abc.jpg
def.jpg
ghi.jpg
But today, instead of creating folders, it is creating 'Package' files, each with a size of 0 bytes.
If I edit the extensions for the names in the list to something like '.png', then it creates a folder. If I have no extension at all, it creates a folder. It's only with '.jpg' that I get the package.
I also find that if I run 'mkdir abc.jpg' it creates a package as well. This is new behaviour and doesn't seem correct to me, as mkdir is a simple and explicit command. As mentioned, the same command with a .png extension works as expected. Also, if I take a folder ending in .png in the Finder and rename it to end with  .jpg, it converts it into a package.
How can I get the terminal to created directories with a .jpg suffix rather than packages? Thanks.

Answer 1

Okay, I think I just discoverd a workaround. This will work if you're lucky enough to already have a smart-mailbox folder that persists after close. (Somehow I had two such folders that already existed and weren't subject to the mysterious disappearances on closing the app; perhaps I created them in a previous OS X release?) Anyway, here goes:
Locate an already existing smart mailbox folder that's working properly. Select the folder (in the sidebar).
Duplicate that folder using the "Duplicate Smart Mailbox" Command. (It's on the contextual pop-up menu or available via the gear icon in the lower left of the window). This should produce and exact copy of the folder and the boxes inside, appearing at the bottom of the smart mailbox list.
Edit the duplicate folder to put the smart mailboxes you want in it, and delete the previous mailboxes (duplicates) that you don't want.
The new folder structure should now persist between launches of the app.
There you go. Not the most elegant process, but workable. Don't know if there's a method if you don't have at least one smart mailbox folder already though.