-snip-
hey, thanks for getting in touch! this could have been a pretty serious bug, but luckily it's not ;-)

the signature is 'base64' encoded which officially should have a trailing '=' if the last 'group' of bytes is only 2 bytes and act as a 'padding' to explicitly declare that you intended the last 'group' to miss 1 byte (base64 is chunked in 3 bytes per 'group') and a trailing '==' when the last 'group' is only 1 byte.
the javascript implementation of base64 actually silently asumes that if you don't have a trailing '=' but the last 'group' is only 2 bytes that it's supposed to be 2 bytes and doesn't error over it.

so when decoded (in javascript) from base64 into binary (or hex) "HyEuQEIIi5KS0dqyCaIWh6a5A3wIMFqkSEehuNa7jOUZTSyLa08czuASi5RUcj78hPI5PMNec0w6Xhz flMbFNcM" and "HyEuQEIIi5KS0dqyCaIWh6a5A3wIMFqkSEehuNa7jOUZTSyLa08czuASi5RUcj78hPI5PMNec0w6Xhz flMbFNcM=" both result in the same data.