Strange result on multiple runs with iPhone 4 iOS 5.1 (Dulles, VA)

[bananabeatz]

When doing several test runs at once using the iPhone 4 iOS 5.1 setting from the Dulles location I'm seeing considerably longer load times (for first view) on the first run than on the subsequent runs.

Example:
http://www.webpagetest.org/result/140405_DG_CF7/

In this test, the first run takes roughly 8 seconds, while the subsequent 7 runs take about 4 seconds or less.

I've tried this on a couple of different sites, and all show the same behaviour. However, it doesn't seem to affect other mobile device settings like the Motorola G or the Nexus 7, which both show consistent load times for first view (see examples below).

http://www.webpagetest.org/result/140405_8F_CGS/
http://www.webpagetest.org/result/140405_KN_CJE/

Does anybody have a possible explanation for the results from the iPhone test?

[pmeenan]

The Android devices are using a newer agent technology and I'm a lot more confident in their results. For the iOS agent it's likely that the OS DNS cache and certificate caches aren't getting cleared so subsequent SSL negotiations will be faster.