I bet your table was created with the “table wizard”. When you inserted the table, you selected some Style different from None (probably Default Style from what I see in the Navigator). This triggers the activation of so-called “table styles” which are not at all styles but a collection of macros.
When you add a row, this addition may need extensive reformatting of the table (e.g. with “styles” exhibiting an alternating row background, a row added in the middle requires a repaint of all rows to cope with parity – strictly speaking only subsequent rows but I guess the wizard is not smart enough for that). Consequently, the macros are relaunched as if the table was just in the process of creation.
You add a row at bottom. The macros are fired and they rebuild the whole table from scratch, not taking into account the styling and other formatting you’ve applied to the table, rows, columns or cells. Your formatting is lost.
In my opinion, the table “styles” are still experimental and not at all integrated in Writer (I mean they don’t preserve user customisation which is a major flaw). You may use them provided you accept them “as is”, without trying to embellish the table (or do that at the very end when your table is no longer modified).
If you intend to “polish” and decorate a table to your taste, insert it with “style” None exclusively. You can then apply styles and they will persist.
Table styles are ill-designed for the majority of cases. Stay away of them if they don’t fit exactly your needs. I call them a specification-bug (which is different from usual implementation-bug). To be really useful, they require a thorough analysis and a complete re-specification.
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