I've noticed that when using HDR bracketing, all images requiring a shutter speed longer than 30 seconds will use the shutter speed set "bulb timer" option. I don't know if this is fixable, but if it was working as expected, it would be useful for those wishing to create an HDR image of a dark scene.
HDR bracketing is set to 0 + ++, 5 shots, 0.5 EV intervals
bulb timer option is set to 3 minutes
the initial shutter speed is 20 seconds
The shutter speeds of the bracketed shots will be: 20s, 30s, 3min, 3min, 3min.
Meanwhile, to some extent, the problem can be worked around by simply making sure that only your brightest exposure will exceed the 30 second mark. Its shutter speed has to be set manually with the "bulb timer" option.
One thing that crossed my mind was extending the list of shutter speeds beyond 30 seconds. But could that solve it?