Cannot create folder consisting of one letter and one number (e.g. "K1")

I want to ceate a new folder.
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When I enter "K1" nothing happens.
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Same for "A1". But after several attempts is suddenly works.

I don't see any problems when trying the same thing here.

Was there any error message?

What kind of drive is involved?

Do you see similar problems if you try making the same names in the same place in File Explorer? It could be something external to Opus blocking the operation or misbehaving.

I think I know what is causing this.

The Opus create Folder dialog shows a list of previously entered folder names.

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If the folder name is in the list, I must press Enter twice to create the folder (sound after first press).
If it is not in the list I only have to press Enter only once.
This is a bit confusing. But in the end I can create the folder and it has nothing to do with two letter folder names.

You can turn it of.