Hi,
Thanks for the kind message. I remember using Sourcesafe integration back in the day, so I know what you mean.
ViEmu, per se, does not try to modify the file at all. When you press RETURN, it just changes the cursor position to the target search match position. In general, the behavior you are getting is not usual for ViEmu.
The problem is most likely due to interactions with VS input handling and the language service. RETURN is usually bound to Edit.BreakLine, the command that inserts a line break in the Visual Studio architecture, and one of the most abused commands by language services, third party add-ins, etc... If you think about it, RETURN usually *does* modify the file. The problem is that ViEmu tries to intercept it and defuse the modification attempt, which it usually can, but it seems in that case it isn't able to.
First question is: what language files are you editing? The Visual Basic language service is one of the usual suspects in these cases, as it's so different from other language support services. Second question is: does the problem happen also if you press RETURN just in normal mode, or in visual mode? Finally, can you open another type of file (say, a raw TXT file, or a file in another language), and check if it happens too? This will also prove valuable in diagnosing the problem.
The problem may also be due to an interaction with another 3rd party add-in, so it would be good to know what other software you are using (Resharper, CodeRush, Visual Assist and other similar tools are likely culprits -- less known tools are more problematic, because I've usually already fixed the interactions with the three main ones I listed). You can try deactivating other plug-ins, or uninstalling them altogether, to try to find the culprit.
Finally, you can go to Tools|Options|Keyboard, and try to unbind Edit.Breakline from RETURN. That may fix it, but it will likely also cause other unwanted side-effects. But it's possibly a worthwhile avenue to explore in fixing the issue.
All in all, I will wait for more info from you to try and diagnose the issue.
Regards and happy new year!
-- Jon