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[inquisitor]

Originally Posted by petkow

Strangely, the "Roaming" IMSI does not register with any local carrier.

That's with intent. Once you register a local IMSI roaming through the "Roaming" IMSI is blocked for that particular country (this has actually been implemented only in early 2012).
As mentioned earlier in this thread the "Roaming" IMSI comes from Vodafone Netherlands and so any airtime generated using the Roaming IMSI must be bought from them. In contrast local IMSIs come from the numerous Lycamobile subsidiaries which can buy the same airtime at significantly lower wholesale tariffs than the earlier because from a technical point of view using local IMSIs is no more roaming but covered by Lycamobile's MVNO wholesale agreement with the local MNO partner.
That said toggle has no choice but to charge higher tariffs when using the Roaming IMSI. Given that most subscribers won't understand the technical background of this multi-IMSI solution there is a significant risk of subscribers using the Roaming IMSI (in particular because the SIM toolkit application does not work reliably on all handsets and so automatic IMSI switching will not work always as in your case) but to expect being charged the local IMSI tariffs.
By disabling roaming through the Roaming IMSI for those countries you have a local IMSI from this risk of unexpected substantially higher charges is eliminated while also increasing revenues of Lycamobile's local subsidiaries.