I just reproduced this behavior on a completely unrelated mediawiki site running on a
Brion, when you reproduced the problem and found it was session-based, is there any
chance that caching might have thrown off your results? Here's what I just noticed:
1. Open Firefox and hit a long-running page (containing <wait>300</wait> or
2. While Firefox is spinning, open IE and hit a different page on the same wiki,
"Foo". Possibly it renders quickly, as you found.
3. But... now force-refresh IE (ctrl-F5) on that same wiki page ("Foo"), or
add action=purge. I find the article does NOT render until Firefox stops spinning,
meaning the <wait> tag is blocking the other session too.
4. Likewise, hit some non-article like Special:SpecialPages while Firefox is spinning.
Again, the page won't render until the article in Firefox does.
Could you check this on your end?
Here's a summary of the problem and my findings. It's still unsolved. Any
Symptom: ALL requests to MW 1.13 time-out while ANY ONE user is hitting a
long-running page (e.g., one with a long-running parser tag)