I noticed the other day, that when I use files in a server based file synchronization environment (ownCloud), .odt files may be transformed immediately or after having been edited a few times into an unknown file format. Usually, I expect to see something like "file.odt" in file explorer, but for some files - I have no idea why this happens only to SOME files - I suddenly get just "file".
When you save a document from an application, the application will normally offer to add the appropriate extension to the file name, so if you save a text file as "file", what you get will be "file.odt". But if you offer an extension, this doesn't necessarily happen, so an attempt to save as "file.odt" does *not* produce "file.odt.odt". Indeed, you can confuse yourself (and perhaps others?) by saving a text file (in ODT format) as "file.ods" or "file.doc"! And including a dot in the file name can sometimes make the application think that you have already provided an extension, so that it doesn't provide one itself.
When I click that file to open it, the computer shows me a list of possibly useful application to choose from to open that file.
Your operating system uses the file name extension to decide what application to use by default to open the document file. If there is no extension, it will ask for advice.
Even creating a new/blank file, copying the text of the original file into a text editor and then from there into the new document produces the same result.
With the same choice of file name, it presumably will. Computers are nothing if not consistent!
Does anybody know WHY this happens - and if possible could tell me how to fix it?
Choose your file names judiciously. Avoid dots unless you know what you are doing.
I trust this helps.