I wasn't familiar with that "-r", but FWIW the gsed man page says "(for portability use POSIX -E)"

Abutting that "r" option against the "i" option is likely why you ended up with a file named .txtr and therefore implies that it did not actually hear the "-r" you intended

I've had the best luck picking an actual backup suffix such as "-i.bak" or "-i~" to keep BSD sed and GNU sed on the same page, although I've also seen scripts that go as far as "--version" sniffing and changing the actual invocation as "${SED_I} -E" type stuff