In using a -07 to replace a low quality USB<>serial interface on a tekpower bench supply with wireless - I ran into this issue due to the tekpower driving the serial input with garbage during power up - which should be ok, after all, it's an ESP input, and the tekpower's PIC chip was just gargling as their init code ran.
This took a whole day to figure out, as after all, who would check if driving an input during init would break something so thoroughly? And what are the odds that the timing of that driving would often match the ESP's timing on *DRIVING A PIN DEFINED AS AN INPUT* during a power up such that it sometimes worked?
Details on my site here - hope it saves some hair pulling in the community.
http://www.coultersmithing.com/forums/v ... 6259#p6259