Custom field "entrytype" resets upon modification

[ThiloteE]

Thank you @ThiloteE , here is a way to replicate the second issue using fresh library.

1. Create a new library
2. Go to Options -> Customize entry types
3. Select Article and click on the drop down list. Please note that there is no Entrytype field available in the drop down list.

4. Type in Entrytype and click on + button

5. Create 2 new articles
6. Navigate to Optional fields.

7. Delete the value in Entrytype at Optional fields
8. Select second entry and reselect first entry
9. The Article value is back in Entrytype at Optional fields. However, it is being deleted in bibtex source.

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My first guess to this issue is that there is an internal EntryType variable that does not allow user to modify it.
However, I could confirm that this second issue does not relate to #8527.
Would really appreciate if it could be moved as separate issue ticket.

Originally posted by @LIM0000 in #8527 (comment)

[ThiloteE]

JabRef 5.7--2022-06-15--cb5fe60
Linux 5.4.0-120-generic amd64
Java 18.0.1
JavaFX unknown

I was able to reproduce by following your steps and creating custom field called entrytype.
I was NOT able to reproduce by creating a custom field called Xyz or Aaaaa.

It did not matter if set as optional field or required field.

So you might be right with

My first guess to this issue is that there is an internal EntryType variable that does not allow user to modify it.

[ThiloteE]

I would suggest to treat this issue with low priority, as this seems to be a severe edge case and a workaround exist:

Workaround:

Simply rename the custom field entrytype to something else. E.g.: CustomEntryType or typeofentry.