At one point in time (approximately a year or more ago) Digi did uncover a manufacturing problem whereby Connect -C modules were shipped out with the default MAC address was incorrectly programmed into units, thus the BA:DB:AD address showed up in the serial dialog. This issue was quickly addressed and processes put into place to help ensure that this issue would not arise.
If, indeed, these modules are 'fresh', meaning that they have never been used to run (by way of the debugger or otherwise) an image developed a using NET+OS development kit, please contact Digi support with the serial numbers of said products. We certain want to address any possible manufacturing problems that may arise.
There is, however, another possible explanation for the MAC address to have been reset. The default application on a factory fresh module was built on NET+OS version 6.0. The BSP, provided with NET+OS versions subsequent to 6.0 (e.g. 6.1, 6.2, 6.3, etc.) are able to recognize a previous NET+OS version's NVRAM structure and convert it. If one, for example, builds and runs an example based on 6.3, using the debugger, the NVRAM structure will be converted to a 6.3 version and re-written to NVRAM. Since the 6.3 application image is not written to flash, when debugging, if one subsequently resets (e.g. power cycles) the module it will boot the 6.0 image, currently stored in flash. Because the 6.0 image is unablle to recognize the 6.3 NVRAM structure format it will erase it and use its pre-detemined defaults (based on appconf.h), in which the aforementioned MAC address (or whatever address is specified in appfconf.h) is used.
There may be other reasons for this resetting of NVRAM, specific to the individual application, which would have to addressed on a case by case basis.
Support phone: (952) 912-3456
Support e-mail: http://www.digi.com/support/supportrequest.jsp