It is probably because in doing so you negate or reset all the existing spherical fall off zones. The reason for the "spikes" is most usually that the original fall off zones are just that little bit too small so some of the cloth gets excluded. The correct adjustment is to increase the scale of these by one or two percent.

Depending on what version of Wardrobe Wizard/Poser you are using an explanatory video is included in the help file. This may be viewed on line at http://www.philc.net/WW2_help.php Scroll down to "Joint Parameters". There is no one size fits all where joint parameters are concerned however I feel that this video simplifies the mystery considerably.