We're using the great Akeeba Ticket System to give our customers support for our products. It's a great tool with a lot of flexible configuration possibilities. To use it correctly we needed to configure the system and set all the security for folder access, uploads of images and other kind of attachments to make things secure.

The Ticket system seemed to work correctly after testing. Creating a ticket, reply to a ticket, upload images or other attachments, all worked well. Let's go live! Great!
Testing is the first step but going live is the real test; in the first days a few little things we're noticed by our users and it was just a matter of fine-tuning some settings. After a few days reports of users started getting in about not being able to upload image attachments.
That's weird and ofcourse I've tried uploading some myself. Hmmm, all seems to work fine - could it be an issue with the user rights? After comparing the user rights and all looked fine I created a new user, created a ticket (as that user) including an image attachment and it does get uploaded correctly?!? I'm fallbergasted...

Back to the drawingboard: check the upload file extensions in the Joomla! Media Manager, because that's responsible for the uploads. The image file extensions like jpg, png and more are present so that should be correct - which I already knew because uploading did work. Well, than it must be some configuration setting in the Akeeba Tickets Syflabbergstem and maybe the Support of Akeeba already has some issues described like this. But, no, the Support from the Akeeba site points to all the configuration settings in the Media Manager, Akeeba Tickets System and the .htaccess file I've already checked ánd double checked! All should work fine so why isn't it?

Just one more test but now I'll use some other pictures (png/jpg) just to see what happends. First attachment file "image01.jpg" was uploaded correctly but than the second file "image02.PNG" returned an upload error: "The file extensions is not allowed!". Do you spot the difference between the two file names? Right! The name of the file extensions, that's true but the other difference? The CAPITAL writing of the file extension!

I went back to the configuration settings of the Media Manager; added the 'PNG' (in uppercase) at the end of the line and tested it. BINGO! The upload with the "image02.PNG" works perfectly.
Now I've added all file extensions in lower- ánd uppercase to the Media Manager configuration so that shouldn't be a problem anymore.

Never thought this would be an issue when using a sophisticated CMS like Joomla! - maybe it can be implemented in the next update so we don't have to add file extensions twice in the Media Manager configuration and prevent brainteasers like this :-)