I ran into this in 9.2 as well (have any Vortx support people read this thread?), but I have the source code so I was able to fix it.
In the MakeOtherMultis function in AppLogic.cs in AspDotNetStorefrontCore, change 2 lines:
Change
Code:
string imagepath = GetImagePath("Product", size.ToString(), true) + FN + "_" + ImageNumber.ToLowerInvariant() + "_" + SafeColor + imgExt;
to
Code:
string imagepath = GetImagePath("Product", size.ToString(), true) + FN + "_" + ImageNumber.ToLowerInvariant() + (size == ProductImageSize.micro ? "" : "_" + SafeColor) + imgExt;
And change
Code:
System.IO.File.Delete(GetImagePath("Product", size.ToString(), true) + FN + "_" + ImageNumber.ToLowerInvariant() + "_" + SafeColor + ss);
to
Code:
System.IO.File.Delete(GetImagePath("Product", size.ToString(), true) + FN + "_" + ImageNumber.ToLowerInvariant() + (size == ProductImageSize.micro ? "" : "_" + SafeColor) + ss);
In both of those, a small check is made to see if we are processing the micro image, and if so, to not put in the underscore and the SafeColor.
The multi image manager will create all other sizes as normal, and won't add the trailing underscore to the micro image file name. Now the rollover images show on the product page and everything seems to work as it should. I really hope this is fixed in the next patch/release as it is such a simple correction.