Ok possible bug. In my config I have it set up to where it is build/buy on current lot always. And when I was testing out the new 1.55 version with my config file set that way it made it to where I could not build/buy at all on houseboats. I didn't notice a problem on regular lots just houseboats. I did try moving the camera all around on the houseboat and even down to the basement and zoomed in, all with the same result the build/buy was totally disabled. No other issues found as of yet. But thought I would let you know about this one. Once I edited by config file turning off that feature I didn't have a problem with build/buy mode.
I also am having this issue. I have turned the build/buy on current lot off. House boats seem to be the only problem with build/buy mode. When I take AM out it works, put it back in, it doesnt work.
I was also having issues with this. However, I just noticed that if I go into Map View, and click the buy / build icons from there, I go into buy / build mode on my houseboat. This works while AlwaysBuildBuyHere is still set to TRUE and TestingCheatsEnabled set to FALSE.