ft-burn? fails with err u1 with no reasonable explanation

[perplexedpigmy]

We had ft-burn? failing with u1 error
As per the documentation
"If a non-positive amount is provided to burn, this function returns (err 1). Otherwise, on successfuly burn, it returns (ok true)."

But neither the amount sent was negative nor the desired amount of tokens owned by the principal and a consecutive ft-burn? went through without any hiccups

Any suggestions?

[perplexedpigmy]

Discussion here
#3460 (comment)