Reber added that he had “nothing but gratitude” for Microsoft, and that he was simply sad Wunderlist didn’t go as planned.

It’s a thorny situation for Microsoft. Wunderlist’s cloud features still run on Amazon Web Services instead of Azure, The Verge noted, but Microsoft can’t easily pull the plug after saying it would only shut down Wunderlist once To-Do had feature parity. At the same time, selling Wunderlist to Reber would create its own complications — To-Do would have a direct competitor using rival services. The founder planned to improve it if he did get control, including improved performance, new features and open source code.

While there aren’t any indications Microsoft is about to take up Reber’s request, this does illustrate the mixed results of the company’s app acquisition spree. Microsoft fared well when it snapped up Acompli to bolster Outlook on mobile. The buyout of Sunrise, however, was less well received — people lamented the loss of Sunrise Calendar even as its features found their way into Outlook. The Wunderlist purchase is somewhere in between. Microsoft may have gone out of its way to keep Wunderlist alive, but its threat of pulling the app has made some people nervous.