Here is a bug report, Andrew:

With the latest sylpheed build, if you open up a composition window and then minimize it (by hitting the minimize button next to the X or by hitting the home button), there doesn't appear to be an easy way to get it back. I lost a fairly long email this way (typed out on the on screen keyboard, no less)...eek! Has anyone tested Sylpheed with a bluetooth keyboard? Any gotchas?