Preparing the test:
1. Edit > Autotext… > Categories…
2. Type in category name, which has no space, for example "testcategory", choose
proper path
3. Click button 'New' and then 'OK'
4. Close dialog
5. Mark part of the text document
6. Edit > Autotext…
7. Click on the category "testcategory"
8. Type in name and shortcut for the new autotext, Click on drop-down 'AutoText'
and there on entry 'New'. Close dialog.
9. Proof your new autotext. It should work.
10. Make a copy of the generated 'testcategory.bau' file.

Reproducing the error:
11. Edit > Autotext… > Categories…
12. Click on category 'testcategory'
13. Enter new name 'test category' and choose the same path as before.
14. Now the button 'Rename' is enabled, click it. You see the new name in the
list. Close dialog with OK.
15. Notice, the category list has got the new name 'test category', but the
category is empty.
16. Close dialog
17. Edit > Autotext…
18. Notice, now you have two entries 'test category'. Both are empty.

Take a file explorer to see what has happend.
You have got a file 'test category.bau' which is an empty autotext file and in
addition a file 'text%20category.bau' which is your old autotext file, whithout
any changies but the file name. You can verify this, if you unpack it.

Doing the same with a new category name without space, works as expected.