Its not really a new announcement but had been announced some time ago -- the changes have just been implemented now. The more important story is the reason behind the management changes, and to what extent it is related to issues with Gafisa's auditor about various possible accounting issues which have been raised -- this is the unknown that is affecting the stock at the moment.
I could not locate any public information regarding accounting irregularities. Do you have a link?
I did locate two pcs of info. pointing toward different reasons.
One is the likely halt and demolition of an office bldg. that should not have gone up where it did next to a heritage site. The issue began in March of last year but appears to be going the wrong way now for GFA: