I can confirm that I get this behaviour as well. It is frustrating (even annoying!). Fortunately, it has been reported as a bug (numerous times) but I think this is the main entry: fdo#115573
According to the comment thread on that ticket, the fix will be available with v. 6.0.3. I’m still on 6.0.2 on both Ubuntu and OSX, so am looking forward to the new release making its way through the pipeline.
Update (2018.04.13) - I just got the update, it is now fixed for documents/tables created in v. 6.0.3+ – that is, if you just load in a doc created in an earlier version (e.g., 6.0.2!), the “bug” will still be present. As noted in comment #17:
Try recreating the table after the patch is applied. You should notice in the sidebar styles table styles that the table style changes from highlighting whatever the initial chosen style is, Default Style if no style is selected when created, to no style highlighted when a change is made to the table using the table properties dialog.
If you copy/paste a table from an old document into a new one, the fix works. If you simply edit the table created in version(s) earlier than 6.0.3., the borked behaviour is still seen, even editing in 6.0.3. I hope that’s clear!