code after vector table ARM A9

Question

I am implementing a small OS as a university project in a A9 chip (a Xilinx Zynq). I am using trustzone to implement some features and I want to pass through SVC calls from user mode directly to monitor, so I issue an SMC in my SVC handler. Here it is a version of the vector table plus handler which works (I removed other handler code for simplicity):

secure_vectors:
    ldr     pc, _secure_reset
    b       _secure_undef
    b       _secure_svc
    b       _secure_prefAbort
    b       _secure_dataAbort
    b       .                           /* reserved for HYP mode - not supported */
    b       _secure_irq
    b       .                           /* reserved for MON mode */

_secure_undef:
    b       .
_secure_svc:
    smc #0
    movs pc, lr
_secure_prefAbort:
    b       .
_secure_dataAbort:
    b       .
_secure_irq:
    b      

However, I am having an issue if I position my handler code immediately after the vector table. If I position the handler as below, sometimes the SMC call is not issued. When debugging I step through the instruction, but it is as if it never happened since the monitor vector table does not receive the SMC exception:

secure_vectors:
    ldr     pc, _secure_reset
    b       _secure_undef
    b       _secure_svc
    b       _secure_prefAbort
    b       _secure_dataAbort
    b       .                           /* reserved for HYP mode - not supported */
    b       _secure_irq
    b       .                           /* reserved for MON mode */

_secure_svc:
    smc #0
    movs pc, lr
_secure_undef:
    b       .
_secure_prefAbort:
    b       .
_secure_dataAbort:
    b       .
_secure_irq:
    b       

Even a "NOP" instruction before the handler solves the problem:

secure_vectors:
    ldr     pc, _secure_reset
    b       _secure_undef
    b       _secure_svc
    b       _secure_prefAbort
    b       _secure_dataAbort
    b       .                           /* reserved for HYP mode - not supported */
    b       _secure_irq
    b       .                           /* reserved for MON mode */

    nop
_secure_svc:
    smc #0
    movs pc, lr
_secure_undef:
    b       .
_secure_prefAbort:
    b       .
_secure_dataAbort:
    b       .
_secure_irq:
    b   

I really don't understand why this happens. Am I missing missing something obvious?