Problems with resized PNG files

[vincenth]

I use PSP to reduce the pixel dimensions of image files (to create thumbnails typically). With certain thumbnails, internet browsers have given me trouble; i.e., they won't display the thumbnail image each time (when the problem occurs in IE8, refresh displays the thumbnail properly, while a second refresh makes it disappear again). This is strange behavior and I'm wondering if I'm selecting less-than-ideal options for re-size.

I use PNG image files, the "Smart Size" for the resize method, always preserve aspect ratio, and typically reduce to 30-50% of the original image dimensions. Any ideas?