Cloaking search engines is a bigger risk than just cloaking Pinterest IMO unless you only get traffic from Pinterest and then you have bigger problems anyway.
The real issue with cloaking, if it's done too rigidly by IP range plus UA, is if they expand their IP range suddenly you're caught exposing your site differently to them depending on which IP range they use. How to handle IP range changes should always be taken into consideration in advance when cloaking.
Sounds like the OP fixed it already so it's not an issue anymore for the OP anyway.
I'm sure others are having this problem too so it's probably not the last we'll hear of it.
So now we know. If you can't get results from support at Pinterest, try their press office.
My support failed email methods usually included email to the CEO, chairman of the board, basically any higher level email address available including PR person and cc: support which usually gets things jumping all over the place.
Nothing tends to impress upon a CEO you're a really unhappy squeaky wheel like spamming a support problem to half their company ;)