Currently, some bbclass or recipes in poky use bash specific syntax, such as [[]]. on some system /bin/sh is not pointing to /bin/bash, thus when bitbake executes any shell pieces of code, it has a chance to fail on those systems. Example of such system can be recent Ubuntu where /bin/sh is pointed to dash.
suggest bitbake can check whether a /bin/sh script contains any bash-specific contructs when parse bb or bbclass.
This is already covered by bug 8851. *** This bug has been marked as a duplicate of bug 8851 ***