IE11 causing double events

Hello,

i'm using JEvents for booking cars in my company.
It works fine, as long as the employee use Firefox for creating a new event.

When ever an employee use the Internet Explorer 11, two identical entries are made.
These double entries are also shown in the MySQL Table.

The screenshot I uploaded shows the problem i have.
I modified some layout files, which I also uploaded.

It isn't possible to post a link of my site, because it is an internal site.

I found some other threads with the same problem, but these couldn't help me.
Are there any workarounds or fixes?

Thanks