If you paste multiple lines of text into a cell, Calc's AutoCorrect will change the first character of the last line to uppercase:

foo  =>  foo
bar      bar
baz      Baz

UI/UX Design by

We make sure that your target audience has the best possible experience with your digital product. You get:

• Design tailored to your audience
• Proven processes customized to your needs
• An expert team of experienced designers

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To fix this, go to Tools / AutoCorrect Options, choose the Options tab and uncheck every box. You're a programmer, you don't need wimpy AutoCorrect assistance.