DIV32 requires that PBP's system variables be loaded with a 32-bit value from a prior 16x16 bit multiplication.
The multiplication has to use at least 1 WORD variable.

But when you specify a multiplication of 2 constants ... the multiplication is done a compile-time as part of the optimization (constant folding).
The system variables never get loaded, because the multiplication was not done at run-time.

The mid-word multiplier is never done at compile-time, even if it has two constants.
It's always done at run-time, and the system variables do get loaded.

And ... TMR1 is declared as a WORD variable in the .pbpinc files.
It's OK to read the entire Timer1 value as long as two conditions are met ... the Timer must be stopped, and RD16 must NOT be set.