I am working on an App connected to SharePoint Lists, so dependant dropdowns, filters, etc. are binded to SharePoint.
The problem (a big one) is that Source code on events such as OnChange and Filters defined as formulas are being replaced with "Title" property when others were written. I noticed it and I thought it was my mistake but I could confirm it is really a bug. I am trying to reproduce it consistently but by now may be it occurs when Properities panel is shifted from simple to Advanced and/or back. It was also noticeable when application was exported and imported in other environment.
I think I found the reason of this behavior (and I think it stills a bug).
SharePoint lists use an internal column name and a display name, in my case I have renamed Title columns to something else, then in PowerApps I referenced that new names and were recognized. When App is reopened, exported/imported or laguage changed, the column name used in PowerApp code is changed to "Title", the internal SharePoint name.