While using the LOOP CATURE [function] and when the SOURCE SELECT is set to EXT ONLY, if you continue to only overdub the external input signal while playing a pad at the same time, we resolved the issue that caused it to occasionally start recording the sound from the pad, which is not supposed to record.
LINK:
http://www.roland.com/products/en/_support/dld.cfm?ln=en&dsp=0&iCncd=2828