Correct transfer function with 1st order IIR filter What diffreneces it makes in magnitude and/or phase response when using 

$$H(z) = \frac{b_0 + b_1z^{-1} + b_2z^{-2}}{a_0 + a_1z^{-1} + a_2z^{-2}}$$ by adding $b_2=0$, $a_2=0$ 

instead of

$$H(z) = \frac{b_0 + b_1z^{-1}}{a_0 + a_1z^{-1}}$$

for 1st order filter?

All software I'm using for to build VST plug-ins (SynthEdit, FlowStone, etc.) implements a biquad (BLT) module for coefficient input and now it looks like I can't get 90° phase response with a filter designed using Octave (by Octave plot phase is 90°).

EDIT: Ok, digged the web a bit more and found these three (1 2 3) articles published at analog.com. Is the situation same with one pole allpass filter vs biquad allpass filter (what are the phase responses for these?)?
If the formula becomes the same, the response becomes the same – there's no difference to be expected.