Parliament on the other hand still appears to be solidly pro-Linux.
We should note the types of complaints: on the one had there are the usual complaints ("it's broken"). These would be the same in an MS Office world. Why? Because most of government office work is based on standardized templates which are custom implementations. These would have to be retrofitted to MS Office in a switch back. There's little reason to assume that they would become any better in that case.
On the other hand, there are complaints about interoperability with the outside world: outside people sending MS Office documents or being unable to read open formats. Yes it's annoying, but if you decide to go with a standard instead of proprietary stuff you expect this. It should be noted that the largest external groups the city of Munich has to deal with are the enveloping government bodies, namely the district of upper Bavaria and the state of Bavaria -- both run by the conservative party of the new 2nd mayor. These never liked non-proprietary software and history ahs shown again and again that they will do whatever they can to make administering a social-democratic town (which Munich still is) a bit more difficult.
Third, the new second mayor complained about something as great as Outlook not being available. So that's the real issue: taking office he had to change his habits, something that by definition is hard for a conservative
As for the new first mayor: he has been a big shot in city administration for a long time, and he has always been outspoken against the Linux switchover. Why would he change his mind now when he has negotiated Microsoft's move into the city from the suburbs?