Following UX/UI patterns make sense, but not design - especially if you plan to be cross platform.
I suppose it makes sense from a branding perspective, but any designer worth their weight should be able to come up with a distinctive branded experience that doesn't revamp the entire, default, builtin experience on the device.
The initial target was iOS and then clients requested Android compatibility as well. Designs for iOS are completed and implemented and are then re-used for Android. The excuse is 'consistent user experience' but really they just don't want to do the same job twice for a platform that generally has less usage and provides less profit (in our case at least).
I took matters into my own hands and there are noticeable differences between the two applications. There was of course some backlash (I flat out refused to put a 'back' button on the action bar for example or move the sliding menu to the right side) but in general the look and feel is consistent across the two platforms.
That doesn't (and won't) stop me from using native controls such as text inputs and dialogs that users on Android are quite familiar with.
In case someone has no clue what the hell I'm talking about I'd be happy to share some screenshots via pm.
Yeah, this is a sign of a bad PM, who doesn't understand the market or mobile ecosystem enough to realize that the targets are completely different.
On the other hand, if the interface was designed to be completely unique and skirted all the specifics of the deployment platform, in an attempt to be branded or for reuse of designs, that's reasonable. Often, however, it is obvious that the design was optimized for another platform than the one you're using it on. "Custom back button" on Android, indeed.