Red dotted frames on blocks even when not editing

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Hello all,

since poking around with the friendly URLs (still not solved: i'm still getting "No input file specified", but that's a different story), as soon as I log in I get the red-dotted frames around the blocks and the "Add to main" / "Add to sidebar" placeholders, even when I am not in editing mode.

What did I do wrong? Is there an easy way to fix this?

Thanks in advance!

Cheers,
Axel