Suggested passwords not accepted by the US State Department's visa appointment service

[domneill]

Passwords suggested by Safari aren't accepted by the State Department's visa appointment service (https://ais.usvisa-info.com)

When I try to create a new password, I'm told it must be at least 8 characters, despite the suggested password meeting that requirement.

I encountered this on the non-immigrant visa page for the US embassy in London (https://ais.usvisa-info.com/en-gb/niv) but it may also apply elsewhere.