That's possibly the case for the first problem Alex mentioned alright but regarding the second issue, there does actually appear to be a problem with the ordinary lasso tool (as opposed to Polyganol and Magnetic). What happened to me was, I'd start making a selection and after about 5 seconds the screen would jump, selection would stop and marching ants would complete itself from that point, giving a very incomplete selection also showing a "Not Responding" message in the top left of the Elements window. Strangely it always happened after about 5 secs so if I made my desired selection within that short time there was no problem. This had nothing to do with layers or feathering being too large as the other two Lasso tools work perfectly. Looking for a solution to the problem on the internet yesterday, it appears there are many others with the same problem....
http://forums.adobe.com/message/3333409
Strange one alright and I'm not sure how or why the operating system fix that I came across has sorted the problem but it certainly worked for me.
Mark