Conditions are set always within a coincidence event. A condition set on an event in ADC1A can be combined with a condition set on an event in ADC1B only for coincidence events when ADC1A and ADC1B have simultaneously an event. What you intend to do is probably better done by a sum of histograms from different ADC's, see the FAQ concerning the 'superdetector'.

A possible way to do what you want is the following:
Create 3 spectra, the first with a condition set on the ROI in 1A, the second with a condition set on the ROI in 1B, and the third with an AND-combination of both ROI conditions. Then save all three spectra into seperated files, say m1a.mp, m1b.mp and m12.mp. Now using the data operations dialog read in m1a.mp as a "new" seperated spectra, then sum m2b.mp to that spectra and finally subtract m12.mp from it, because otherwise the coincidence events would be contained twice in the spectra. That's it.