It does indeed sound surprising. This is not meant to be sarcastic, but one imagines those clever engineers might have thought of seals and insulation to protect the Kaiser's investment, so to speak
I would sort of agree, but it is not easy to make a ship fully watertight and provide the old voice pipe communications to everywhere below decks, and any seal will eventually fail or decay. The worst problems seem to occur after battle damage when the frame can distort, all the German ships showed a tendancy to progressive flooding to some degree, but it would take a naval architecht to explain it properly. Goodall's report is available online, but only to people belonging to a naval architechts site which has a sizable fee attached. One poster had seen the report as he was a naval architecht, did post some details years ago. If he is still online he maybe happy enough to discuss it with you, his name is Stuart Slade, but I have no real idea where he may post now as we lost contact some years ago.
Do you know if British ships had the same problem?
British ships were also to suffer similar problems, the Audacious being the most notable as she struck a single mine and took hours to sink. This was largely due to being unable to make her watertight properly, some areas (doors and deck hatches) had corrosion that prevented a proper seal and so on. This would be more understandable if she had not been a new ship! In the Victorian navy HMS Victoria sank after being rammed, but the flooding was very rapid as many doors and portholes would no longer close, some due to rusting and some reportedly due to paint!