Hi
I have the same issue - almost anyway - mine happends right after a table.
In my case it happends in a template on one line only - so I have lines that work fine and doesn't get new font type - both after and before, where I use a combination of text from the template and replaceVariableByText.
I replace many variables in the template and your examples does not cover this and I don't want to define a font type for each context - that would be crazy.
Have downloaded latest version of MultiMerge.inc.
Sure I can probably find a workaround and will have to - since none of the solutions suggested works for me, but you have to look into this as an error - because that is what it is.
EDIT: Now I have done a bit more investigation and it seems a lot like the error is related to replaceVariableByText for me. The method replaceTableVariable is for example not getting overwritten on merging in any cases