Bulb setting on e520
I don't believe you're doing anything wrong.
The camera is taking a dark frame after your first exposure, and using that to subtract the electronic noise from your long-exposure image. I'm afraid that's exactly how it works.
If you turn off Noise Reduction (vice Noise Filter), it'll let you take another shot, but your images will be very noisy.
|Bianca Buitendag-7809 by vbuhay|
|Sunrise in Paradise by OB Foto|
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|The Battle for the Lead by Photo Pete|
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|Cecelia's Eyes by Madeleine Hart|
from - Jenny from the Block - (Colors that pop + A white Border)