Quite so - don't worry about being asked for more evidence. This is a normal part of processing. It can happen for two reasons. One is if, as he goes through your case, he finds there isn't enough information to allow him to tick off some point as verified. The second is that COs routinely ask for more partnership proof, to cover the time while the application has been being processed, just before they issue the visa. This is to make sure that they don't give a visa to somebody whose relationship has broken down in the meantime.