I tried replying to this a few times because it's fairly important but kept failing to express it in any coherent manner!
I havn't really had any problems with PayPal as such - they offer a lot of convenience and 99% of the times I've had no problems with them (having my steam account blocked was one - but I think that was less to do with PayPal). Particularly useful is that I have an touch pay access card (where you just tap it on the card machine) so I can spend my PayPal balance to buy lunch/beer or buy stuff with a PIN number.
PayPal are a huge company and must deal with and process so much money so I guess they have a lot of responsibilities to comply with so they probably err on the side of caution a lot of the time so they don't land themselves in serious trouble for not complying with national & international laws. Not to mention they probably have a responsibility to tax / money laundering laws as well - I'd imagine it's a huge legal minefield for them!!
It doesn't seem that this relates particularly to crowd-funding and more to do with large payments being sent/received - it probably happens automatically in a similar way to when your card gets automatically cancelled if they suspect fraudulent purchases.
The fact these people don't have any way of getting in touch with someone at PayPal is pretty terrible though. I remember having problems with a gmail account vanishing (literally - one day I couldn't login and never had access to it ever again!) and had no way of getting in touch with someone.
In any case...they apparently announced today that they are going to do 'something' about it!
http://www.engadget.com/2013/09/13/paypal-revamping-its-policies-to-better-support-crowdfunding/?utm_medium=feed&utm_source=Feed_Classic&utm_campaign=Engadget&ncid=rss_semi