escape & in substitution in fakevim mode

In fakevim mode, vim command line handles '&' in substitution strangely. For example, I want to replace all 'a' with '&' in a line,

:.s/a/\&/g

this works in vim, but gives me '\&' in fakevim. of course,

:.s/a/&/g

is essential no-op.

Fakevim should handle escape of & as in vim