ibwt() / ibrd() immediatly following ibclr()

I have some code that writes an "IDN?" and reads the requested string from a device.
I issue an ibclr() immediately before the ibwt(). It seems that if I do this, I receive an error (2 - 'You have attempted to write data or command bytes, but there are no listeners currently addressed.').
If I add a ~20ms delay after the ibclr(), before the ibwt(), then it works as expected.

Is this a problem with the device ? (HP8753b) or in the driver (or my approach).

Michael