Version:            (using KDE 3.5.9)
Compiler:          gcc version 4.1.2 
OS:                Linux
Installed from:    Gentoo Packages

For more than a year I've had the problem that attempts at opening PDF, JPG, DVI, ODT, DOC etc. files from the web have often stalled at just a few percent, but have eventually opened if the link is clicked several more times (and then all the attempts open at once).

Before reporting this, I've made a thorough investigation on two computers on different networks, after removing all config files.  The result is that I've identified the problem as occurring WHEN and ONLY WHEN  konqueror is configured to open a filetype in an external viewer, e.g. kpdf, kuickshow, AND there is a proxy server.  

It doesn't matter which external viewer.  The only proxy I've used is squid; at one place it's a transparent proxy in the gateway, and at the other it's configured in konqueror as a http proxy on port 3128.  I've had several squid versions during the time of the problem, always taking the latest that gentoo-stable can offer. The problem doesn't occur with any other browser I've tried, e.g. firefox, seamonkey.  Loading files into konqueror's embedded viewers never shows the problem.  There's no website that I recall as avoiding this problem, as long as the files are quite large, i.e. hundreds of kB or some MB.  The problem occurs even with a completely new user account, as soon as the external viewer and proxy server settings are applied.

Even with the proxy present, the problem doesn't always happen, 
especially if the file is already cached. I did my testing by opening loads of ~500KB--1500KB jpegs in kuickshow from a page full of pictures.  With the proxy active, the first few attempts went well, then there were about as many failures and successes after that.  Turning off the proxy or turning on embedding allowed tens of successful openings with never a sign of trouble. I tried it a lot of times -- I'd already been trying with loads of other settings such as cache, plugins, etc.

Does this funny combination of circumstances give a hint to any developer as to the difference between downloads to external and embedded viewers?  I'd love to have it fixed, but for now, having discovered the combination, I'll turn off proxies.  I can't stand the other browsers!