One extra character for site key, but still it's working

I have added one extra character ‘i’ at the end of siteKey. But still it’s working fine, but if I add two characters, it shows error. Is it known issue?

Actual Site Key: 0x4AAAAAAAWnxyibCPogKljE
But it works for both 0x4AAAAAAAWnxyibCPogKljEi and 0x4AAAAAAAWnxyibCPogKljE.