Hmm I don't really understand, I have this at the beginning of my code during initialization:

Code:
T1CON = %01101011 'Set Timer prescaler to /4 and enable Timer1 on external 32768Hz crystal
T1OSCEN = 1 (secondary 32768Hz oscillator is enabled)
TMR1CS = 1 (timer clock source is secondary 32768Hz oscillator)

My setup already use the Timer1 for both interrupt and general clock source when in low power mode, and it does work as expected.

I tried to add that T1CON configuration line above my @ SLEEP instruction but that didn't help much. If the SLEEP mode actually turn off all clocking sources then T1OSCEN bit should be set to 0 as well.

Maybe using the IDLE mode and manually disable all peripherals that are enabled default would be a workaround.