We have been building huge websites with Quark since 6.x and have never had that problem, so I think it is systemic in nature.
When any application starts to misbehave wildly like that, I run MacHelpMate or Yasu or some other such utility, lose all the caches, restart and all is well again. When that fails, I unplug EVERYTHING fromt he computer including the power, Ethernet...everything. Plug it all back in, restart and everything magically works like it should. That process neatly resets important stuff under the hood and is why your computer oftern works fine at the shop when it did not work for you on your desk. (I learned this trick from my computer consultant and it has saved me lots of time and hair as well as dollars.)
I hope this works for you.