This is actually not a bug of SharpDevelop, but I ran into troubles getting SharpDevelop to run when the Visual Studio "14" CTP (CTP4 in my case) and the .NET Framework vNext (v4.5.3) are installed. The issue: It erroneously reports you were using a version of .NET that is older than the v4.5 RC, and quits.
The reason is that the assemblies of the .NET Framework vNext have a product version number of v4.0.30319.0 (the file version number is v4.5.19.0), and because of the release number being zero, SharpDevelop assumes the version of .NET is too old, hence the CheckEnvironment method within SharpDevelopMain fails.
So I quickly patched the SharpDevelop.exe using IDA, altering the ldc.4 instruction that loads the integer for the release number to load zero, and now it works again. But for people who'd like to use SharpDevelop alongside the VS "14" CTP, I'd recommend to build their own version of SharpDevelop from the source code and modify the CheckEnvironment method for the time being.