The CSV Import doesn’t set the “LabelOnly” flag. Exporting a Checklist containing an item with the flag “Label Only” and reimporting the CSV again will leave the “Label Only” flag of the item unset. The “Label Only Background color” is imported correctly though…
What value are you putting for the Label Only? All of the boolean values need to be TRUE or FALSE, and all caps.
Also, after your bug report, I did see an issue with the export. A new build Version 2.7.2.508 was just released fixing this. If you do a test and export again, and change a Label Only to TRUE and then re-import you should see the flag get set properly.
Originally I tried the import with the lower case true/false like the export generated. Changing it to upper case solved the issue.
However, I noticed another issue with the import. It seems that the three “link” fields of the items (LinkOnCheck, LinkTarget, LinkAction) aren’t imported. At least they weren’t imported in my case and also the fields were gone on my test case (export - import - export - diff both CSVs).