I just updated MeGUI (which is running on 3 different PCs) and since the update (now to version 0.3.2.0), the DAR setup in the AVS script creator appears to generate the right DAR (in the most recent case, the code generated is:

Code:
# Set DAR in encoder to 144 : 79. The following line is for automatic signalling
global MeGUI_darx = 144
global MeGUI_dary = 79
for a standard 16:9 HD conversion to MKV. If I check the AVS file from previous conversions, it has previously read:
Code:
# Set DAR in encoder to 31 : 17. The following line is for automatic signalling
global MeGUI_darx = 31
global MeGUI_dary = 17
which doesnt necessarily make sense, but the AR was correct previously. Has anyone else seen this odd behavior in MeGUI?

(as a side note, I found that if I removed the signalling information, the AR of the MKV created is correct. Additionally, it's possible to fix the incorrect AR with MKVMergeGUI, if needed - but, of course, we shouldnt need to do so)