Vyper is a Pythonic Smart Contract Language for the ethereum virtual machine. In versions 0.3.1 through 0.3.7, the Vyper compiler generates the wrong bytecode. Any contract that uses the raw_call with revert_on_failure=False and max_outsize=0 receives the wrong response from raw_call.

Depending on the memory garbage, the result can be either True or False. A patch is available and, as of time of publication, anticipated to be part of Vyper 0.3.8. As a workaround, one may always put max_outsize>0.