(Maybe a new with mw 1.24) Site,preloadpageds only yields 1 item. Sample as follows:

import pwb
import pywikibot as py
s = py.Site('bar')
pagenames =['Haiku', 'Homer', 'Ilias', 'Watzmo', 'Wean']
pagelist = [py.Page(s, name) for name in pagenames]
gen = s.preloadpages(pagelist)
for p in gen:

print p.title()
Retrieving 5 pages from wikipedia:bar.
Haiku

the request was /w/api.php?maxlag=5&format=json&rvprop=ids|flags|timestamp|user|comment|content&prop=revisions|info|categoryinfo&titles=Homer|Ilias|Watzmo|Wean|Haiku&meta=userinfo&indexpageids=&action=query&uiprop=blockinfo|hasmsg

inserting direct request call into preloadpages with

data = rvgen.request.submit()
print '#### ####', len(data)

gives me

1

Version: core-(2.0)
Severity: major