the events in that ics file do not have any UIDS. These are required by the spec.
And practically they are essential to detect updates or mods on a single date within a recurring sequence (which could be a change in the summary 0f the event). Since all your UID's are 'empty', it looks like the plugin is matching the events on same day up ('matching' UIDS) and just presenting one of them. Ensuring that the ics file meets the ICS spec should fix that.
According to the spec, each event is required to have a universal identifier. see http://tools.ietf.org/search/rfc5545#page-117
For some reason the ics validator tools are not picking up on this.
Format Definition: A "VEVENT" calendar component is defined by the
eventc = "BEGIN" ":" "VEVENT" CRLF
"END" ":" "VEVENT" CRLF
eventprop = *(
; The following are REQUIRED,
; but MUST NOT occur more than once.
dtstamp / uid /
NOte (amr-events) generates correct ics feeds :-).