So as @jyijyi said the number of CID’s available to work with varies depending on the KCARRIERCFG command setting which is dicussed in the customisation APN, in this APN in table 2 row 4 (not counting the header) it shows the numbers of CID’s available for use for a given carrier config, for the default there is 1 and 2.
What you are asking for is for the number of CID’s available to be used/set to be expanded to the theoretical 15, not for it to be ‘fixed’ as this is documented behaviour and so consequently it is not a bug.
Regards
Matt