I believe it has to do with the way you last accessed your iPod. If you open your iPod and select songs and then select a song to play, the next time you search for a song, it will continue to play through all of your songs. If the last time you accessed the iPod by going to a particular album or playlist, it will only play the songs located in the same album or playlist as the song you searched for.
Its a little confusing but I could try to explain it better if you need me to.
The iPod app is contacting iTunes server to get some encrypted keys. Three of them actually, respectively called "signature", "certs" and "bag". All of them are part of an xml (plist) file located at http://ax.init.itunes.apple.com/bag.xml?ix=2.
There's no POST data, just some cookies and HTTP headers giving information about the device and the context. These informations are part of many request made to Apple servers by iOS.
I have no idea what this "bag" can be nor what it's used for.
Details
Here's the request headers :
User-Agent : iTunes-iPhone/4.3.4 (4; 32GB)
Accept-Language : fr;q=1.0,en;q=1.0[...]
X-Apple-Store-Front : [cut]
X-Apple-Connection-Type : WiFi
X-Apple-Cuid : [cut]
X-Apple-Software-Cuid : [cut]
X-Dsid : [cut]
X-Apple-Client-Application : MediaPlayer
X-Apple-Client-Versions : iBooks/1.3
The cookies names :
mz_at1
s_vi
dssid2
mz_pc
mz_at0
ds01_a
Pod
s_vnum_us
s_vnum_befr
mz_if
mz_pt
a
s_vnum_fr
s_cvp35b
And the XML scheme :
<!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
<key>signature</key>
<data>[encrypted string]</data>
<key>certs</key>
<array>
<data>[encrypted string]</data>
</array>
<key>bag</key>
<data>[VERY long encrypted string]</data>
</dict>
</plist>
The "certs" part seems to be constant, even with a standard browser and none of the special HTTP headers or cookies.
(I don't want to publish too many details as I don't know what they contain about me or my Apple ID.)
Best Answer
You can't really transfer apps between two IOS devices with different Apple IDs, unless you are up for jailbreaking, then I cant help you.
If you want to get the version your son uses on your daughter's device you will need to sign into the App Store with the AppleID on his device. But that will give you all of his settings as well. As you can see, problematic.
However you mention an older version and the App Store will always download the most recent version compatible with your system. So you may end up with the same version you don't want.
Perhaps there is someone else who knows a trick or two that I am not aware of, but if not you may be out of luck.