Microsoft started acting like IBM from the moment the DOS licensing was agreed with IBM. Incredibly naive on IBM's part, or perhaps they simply expected to sell so few machines it wouldn't matter. After all the first PC was deliberately crippled to stay away from more expensive IBM kit.

MS were acting like mini IBM throughout the 80s, and before the mid 80s had very much gained a negative reputation globally. It was against Microsoft, not IBM, that was the usual target of complaint when the first AT clones were coming out - 84? 85? I think Windows 1 was about the same time. Certainly enough of a reputation to be amazed they were still collaborating with IBM to produce the first OS/2, again around the mid 80s.