By entering the silly value 2147483647 into one of the size axes of the test instance block's screen, the structure outline flips for that specific axis. This can occur because unlike structure blocks, the size of a game test structure isn't validated and clamped. This issue does appear to not occur for lower sizes.

I would probably expect the value to be clamped, since a max-integer structure template is completely useless.

(This theoretically would also happen with a modified client sending packets as it seems the size isn't checked for validity, but they would need operator either way)

Relates to MC-269744