Following up on this. I have noticed an issue with smart stacks as well except in my case I have not broken something containing them. Let me be more specific. I am taking a stack of x amount of a resource and putting with another stack containing x amount. Where the sum of the two is <99. Originally, I believe it was caused by patching however, I used up the stacks that had the issue after 149 was pushed, and it happened again while you guys were out. I can't find a common patter to when it happens. It is infrequent, fantastic for troubleshooting, I know. I just notice it when I put items into my stacks on my bookshelves. I am very organized. So each block has only one place I put it and when they won't stack I notice it. Resources I have noticed it occurring with;
compact soft coal
There is also another issue of lower importance. Where you attempt to combine two stacks who's sum would be greater than 99 and you can not stack unless you break them apart manually and combine to a sum of 99 or less.