Avoid re-using cached parse information when parsing the project after a debug/release switch.

src/Main/Base/Project/Src/Services/ParserService/IParserService.cs

@@ -242,8 +242,10 @@ namespace ICSharpCode.SharpDevelop.Parser
 		bool HasParser(FileName fileName);
 		
 		/// <summary>
-		/// Clears the cached parse information.
+		/// Clears the cached parse information for the specified file.
 		/// If the file does not belong to any project, this also clears the cached type system.
+		/// If the file belongs to a project, the cached type system is kept (so that the classes don't go missing from the project),
+		/// but the next ParseFile() call will cause it to be reparsed even if it is unchanged.
 		/// </summary>
 		void ClearParseInformation(FileName fileName);
 		

src/Main/Base/Project/Src/Services/ParserService/ParseProjectContent.cs

@@ -358,6 +358,9 @@ namespace ICSharpCode.SharpDevelop.Parser
 					CancellationToken = progressMonitor.CancellationToken
 				},
 				fileName => {
+					// Clear cached parse information so that the file is forced to be reparsed even if it is unchanged
+					parserService.ClearParseInformation(fileName);
+					
 					ITextSource content = finder.Create(fileName);
 					if (content != null) {
 						parserService.ParseFile(fileName, content, project);

src/Main/SharpDevelop/Parser/ParserServiceEntry.cs

@@ -119,6 +119,8 @@ namespace ICSharpCode.SharpDevelop.Parser
 						entries[i] = new ProjectEntry(oldEntry.Project, oldEntry.UnresolvedFile, null);
 					}
 				}
+				// force re-parse on next ParseFile() call even if unchanged
+				this.currentVersion = null;
 			}
 		}